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Cook County, Illinois
Richard J. Daley Plaza.jpg
Frank LLoyd Wright Studio Chicago Frontage.jpg
Evanston, IL Aerial View.jpg
Montrose Beach.JPG
From top, left to right: Cook County Circuit Court at Daley Center with Chicago Picasso, Frank Lloyd Wright's Studio, Forest Preserve, aerial view of Downtown Chicago, aerial view of Evanston, Montrose Beach in Chicago
Flag of Cook County, Illinois
Official seal of Cook County, Illinois
Location within Illinois
Location within Illinois
Illinois' location within the United States
Illinois' location within the United States
Country United States
State Illinois
Region Northern Illinois
Metro area Chicago Metropolitan
Incorporated January 15, 1831; 193 years ago (1831-01-15),
Named for Daniel Cook
County seat Chicago
Largest city Chicago
Incorporated municipalities
 • Type County
 • Body Board of Commissioners
 • County 1,635 sq mi (4,230 km2)
 • Land 945 sq mi (2,450 km2)
 • Water 690 sq mi (1,800 km2)
 • Metro
10,874 sq mi (28,160 km2)
Area rank 6th largest county in Illinois
Highest elevation
950 ft (290 m)
Lowest elevation
580 ft (180 m)
 • County 5,275,541
 • Density 3,226.6/sq mi (1,245.8/km2)
Time zone UTC−6 (Central)
 • Summer (DST) UTC−5 (Central)
ZIP Code prefixes
Area codes 224/847, 312/872, 773/872, 708
Congressional districts 1st, 2nd, 3rd, 4th, 5th, 6th, 7th,
8th, 9th, 10th and 11th
FIPS code 17-031
GNIS feature ID 1784766
Interstates I-55.svg I-57.svg I-80.svg I-88.svg Chicago Skyway logo.svg I-90.svg I-94.svg I-190.svg I-290.svg I-294.svg I-355.svg
U.S. Routes US 6.svg US 12.svg US 14.svg US 20.svg US 30.svg US 34.svg US 41.svg US 45.svg US 66 (historic).svg
State Routes Illinois 1.svg Illinois 7.svg Illinois 19.svg Illinois 21.svg Illinois 25.svg Illinois 38.svg Illinois 43.svg Illinois 50.svg Illinois 53.svg Illinois 56.svg Illinois 58.svg Illinois 59.svg Illinois 62.svg Illinois 64.svg Illinois 68.svg Illinois 72.svg Illinois 83.svg Illinois 110.svg Illinois 171.svg Illinois 390.svg Illinois 394.svg
Airports Chicago O'Hare International
Chicago Midway International
Chicago Executive
Lansing Municipal
Schaumburg Regional
Major Waterways Lake Michigan – Chicago River
Chicago Sanitary and Ship Canal
Calumet River – Des Plaines River
North Shore Channel

Amtrak stations Chicago Union Station
Glenview – Homewood
La Grange – Summit
Public transit Chicago Transit Authority Logo.svg
Metra Logo without slogan.png

Cook County is the most populous county in the U.S. state of Illinois and the second-most-populous county in the United States, after Los Angeles County, California. More than 40% of all residents of Illinois live within Cook County. As of 2020, the population was 5,275,541. Its county seat is Chicago, the most populous city in Illinois and the third-most-populous city in the United States.

Cook County was incorporated in 1831 and named for Daniel Pope Cook, an early Illinois statesman. It achieved its present boundaries in 1839. During the first half of the 20th century it had the absolute majority of Illinois's population. Within one hundred years the county recorded explosive population growth going from a trading post village with a little over 600 residents to four million citizens, rivalling Paris by the Great Depression.

There are more than 800 local governmental units and nearly 130 municipalities located wholly or partially within Cook County, the largest of which is Chicago. The city is home to approximately 54% of the entire county's population. The part of the county outside of the Chicago and Evanston city limits is divided into 29 townships; these often divide or share governmental services with local municipalities. Townships within Chicago were abolished in 1902 but are retained for real estate assessment purposes. Evanston Township was formerly coterminous with the City of Evanston but was abolished in 2014. County government is overseen by the Cook County Board, and countywide state government offices include the Circuit Court of Cook County, the Cook County State's Attorney, the Cook County Sheriff, and the Cook County Assessor.

Geographically, the county is the sixth-largest in Illinois by land area and the largest by total area. It shares the state's Lake Michigan shoreline with Lake County. Including its lake area, Cook County has a total area of 1,635 square miles (4,234.6 km2), the largest county in Illinois, of which 945 square miles (2,447.5 km2) is land and 690 square miles (1,787.1 km2) (42.16%) is water. Land-use in Cook County is mostly urban and densely populated. Within Cook County, the State of Illinois took advantage of its Lake Michigan access and the Chicago Portage, beginning with the construction of the Illinois and Michigan Canal in 1848. This helped make the region a central transit hub for the nation. Chicago, with its location on the Great Lakes and via the St. Lawrence Seaway, is a global port city, giving Cook County an international shipping port.

Cook County's population is larger than that of 28 different U.S. states and territories, and larger than the population of 11 of the 13 Canadian provinces and territories. Cook County is included in the Chicago metropolitan Combined Statistical Area (CSA), which has a population of approximately 10 million people.


Cook County was created on January 15, 1831, out of Putnam County by an act of the Illinois General Assembly. It was the 54th county established in Illinois and was named after Daniel Cook, one of the earliest and youngest statesmen in Illinois history. He served as the second U.S. Representative from Illinois and the state's first Attorney General. In 1839, DuPage County was carved out of Cook County.


According to the U.S. Census Bureau, the county has a total area of 1,635 square miles (4,230 km2), of which 945 square miles (2,450 km2) is land and 690 square miles (1,800 km2) (42.2%) is water. It is the sixth largest county in Illinois by land area, and the largest in total area. Most of the water is in Lake Michigan. The highest point is more than 950 feet (290 m), and is in northwest Barrington Township, in the northwest corner of the county. The lowest point is less than 580 feet (180 m), along the Lake Michigan shoreline.

Climate and weather

Weather chart for Chicago, Illinois
temperatures in °F
precipitation totals in inches
source: The Weather Channel

In July, temperatures in Chicago, Cook County average daytime highs of 84 °F (29 °C), and nighttime lows of 68 °F (20 °C); and January daytime highs of 31 °F (−1 °C), and nighttime lows of 18 °F (−8 °C). Winter temperatures will sometimes veer above 40 °F (4 °C), and, although not common, have also risen over 50 °F (10 °C) on some winter days. Average monthly precipitation ranged from 4.30 inches (109 mm) in June to 1.77 inches (45 mm) in February.

Major highways

  • I-55.svg Interstate 55
  • I-57 (IL).svg Interstate 57
  • I-80.svg Interstate 80
  • I-88 (IL).svg Interstate 88
  • I-90 (IL).svgI-94.svgChicago Skyway logo.svg Interstate 90 / Interstate 94 / Chicago Skyway
  • I-190 (IL).svg Interstate 190
  • I-290.svg Interstate 290
  • I-294 (IL).svg Interstate 294
  • I-355 (IL).svg Interstate 355
  • US 6.svg U.S. Highway 6
  • US 12.svg U.S. Highway 12
  • US 14.svg U.S. Highway 14
  • US 20.svg U.S. Highway 20
  • US 30.svg U.S. Highway 30
  • US 34.svg U.S. Highway 34
  • US 41.svg U.S. Highway 41
  • US 45.svg U.S. Highway 45
  • US 66 (historic).svg Historic U.S. 66
  • Illinois 1.svg Illinois Route 1
  • Illinois 7.svg Illinois Route 7
  • Illinois 19.svg Illinois Route 19
  • Illinois 21.svg Illinois Route 21
  • Illinois 25.svg Illinois Route 25
  • Illinois 38.svg Illinois Route 38
  • Illinois 43.svg Illinois Route 43
  • Illinois 50.svg Illinois Route 50
  • Illinois 53.svg Illinois Route 53
  • Illinois 56.svg Illinois Route 56
  • Illinois 58.svg Illinois Route 58
  • Illinois 59.svg Illinois Route 59
  • Illinois 62.svg Illinois Route 62
  • Illinois 64.svg Illinois Route 64
  • Illinois 68.svg Illinois Route 68
  • Illinois 72.svg Illinois Route 72
  • Illinois 83.svg Illinois Route 83
  • Illinois 110.svg Illinois Route 110
  • Illinois 171.svg Illinois Route 171
  • Illinois 390.svg Illinois Route 390
  • Illinois 394.svg Illinois Route 394

Adjacent counties


Cook County is among the few counties in the United States to border two counties with the same name (Lake County, Illinois and Lake County, Indiana). Illinois has two such counties (Randolph County borders both Perry County, Illinois and Perry County, Missouri).

National protected area


Historical population
Census Pop.
1840 10,201
1850 43,385 325.3%
1860 144,954 234.1%
1870 349,966 141.4%
1880 607,524 73.6%
1890 1,191,922 96.2%
1900 1,838,735 54.3%
1910 2,405,233 30.8%
1920 3,053,017 26.9%
1930 3,982,123 30.4%
1940 4,063,342 2.0%
1950 4,508,792 11.0%
1960 5,129,725 13.8%
1970 5,492,369 7.1%
1980 5,253,655 −4.3%
1990 5,105,067 −2.8%
2000 5,376,741 5.3%
2010 5,194,675 −3.4%
2020 5,275,541 1.6%
U.S. Decennial Census
1790–1960 1900–1990
1990–2000 2010–2019

According to the 2000 Census there were 1,974,181 households, out of which 30.9% had children under the age of 18 living with them, 44.0% were married couples living together, 15.6% had a female householder with no husband present, and 35.7% were non-families. 29.4% of all households were someone living alone including 9.3% who were 65 years of age or older. The average household size was 2.68 and the average family size was 3.38.

USA Cook County, Illinois age pyramid
2000 census age pyramid for Cook County

In the county, the population age distribution was: 26.0% under the age of 18, 9.9% from 18 to 24, 31.7% from 25 to 44, 20.7% from 45 to 64, and 11.7% who were 65 years of age or older. The median age was 34 years. For every 100 females, there were 93.9 males. For every 100 females age 18 and over, there were 90.5 males.

The median income for a household in the county was $45,922, and the median income for a family was $53,784. Males had a median income of $40,690 versus $31,298 for females. The per capita income for the county was $23,227. About 10.6% of families and 13.5% of the population were below the poverty line, including 18.9% of those under age 18 and 10.3% of those age 65 or over.

As of the fourth quarter of 2021, the median home value in Cook County was $299,571, an increase of 11.7% from the prior year.

According to Census Bureau estimates, the county's population had decreased by 3.4% between the 2000 census and the 2010 census (5,194,675). The county's population had grown slightly again by 2017 (5,211,263).


Demographics (2010)
White Black Asian
55.4% 24.8% 6.2%
Islander Native Other Hispanic
(any race)
0.0% 0.4% 13.1% 24.0%

As of the 2010 Census, the population of the county was 5,194,675, White Americans made up 55.4% of Cook County's population; non-Hispanic whites represented 43.9% of the population. African Americans made up 24.8% of the population. Native Americans made up 0.4% of Cook County's population. Asian Americans made up 6.2% of the population (1.8% Indian, 1.2% Filipino, 1.2% Chinese, 0.7% Korean, 0.3% Vietnamese, 0.2% Japanese, 0.8% Other). Pacific Islander Americans made up less than 0.1% of the population. People from other races made up 10.6% of the population; people from two or more races made up 2.5% of the county's population. Hispanics and Latinos (of any race) made up 24.0% of Cook County's population.

As of the 2000 Census, there were 5,376,741 people, 1,974,181 households, and 1,269,398 families residing in the county. The population density was 5,686 people per square mile (2,195/km2). There were 2,096,121 housing units at an average density of 2,216 per square mile (856/km2). The racial makeup of the county was 56.27% white, 26.14% Black or African American, 0.29% Native American, 4.84% Asian, 0.05% Pacific Islanders, 9.88% from other races, and 2.53% from two or more races. 19.93% of the population were Hispanic or Latino of any race. 9.1% were of Polish, 8.1% German, 7.9% Irish and 5.7% Italian ancestry. 17.63% reported speaking Spanish at home; 3.13% speak Polish.

Whites (Hispanic and non-Hispanic) number roughly 2,793,500. There are about 2,372,500 non-Hispanic whites residing in Cook County. Sizeable non-Hispanic white populations are those of German (11.4%), Irish (10.3%), Polish (9.7%), Italian (6.1%), and British (4.1%) descent. There are also significant groups of Swedish (1.5%), Russian (1.5%), French (1.3%), Greek (1.2%), Czech (1.0%), Dutch (1.0%), Lithuanian (0.9%), and Norwegian (0.8%) descent.

Black Americans are the second largest racial group. Black Americans form over one-quarter (25.4%) of Cook County's population. Blacks of non-Hispanic origin form 25.2% of the population; black Hispanics make up the remaining 0.2% of the populace. There are roughly 1,341,000 African Americans of both Hispanic and non-Hispanic origin living in Cook County; 1,328,000 are non-Hispanic blacks. Roughly 52,500 people were of Sub-Saharan African ancestry, making up 1.0% of the total population.

Approximately 10,300 residents of Cook County are of Native American ancestry. They consist of Cherokee, Chippewa, Navajo, and Sioux. Native Americans of Hispanic origin represent a sizeable portion of the Native American population. Nearly 6,000 Native Americans are of non-Hispanic origin, and some 4,300 are of Hispanic origin. Over 40% of the Native American racial group is of Hispanic descent.

Bar Chart of Non-English Speakers in Cook County, Il (2015)
Non-English speakers in Cook County

Asian Americans are a very sizeable racial group in the county, numbering about 301,000. The Asian population is ethnically diverse, and includes roughly 87,900 Indians, 61,700 Filipinos, 60,700 Chinese, 35,000 Koreans, 13,700 Vietnamese, and 11,100 Japanese. Roughly 30,800 are of other Asian ethnic groups, such as Thai, Cambodian, and Hmong.

Approximately 3,000 residents are of Pacific Islander heritage. This group includes roughly Native Hawaiians, Guamanians, Samoans, and various people of other Pacific Islander groups.

Hispanic and Latino Americans make up over one-fifth (22.8%) of Cook County's population. Roughly 1,204,000 Latinos live in the county. Mexicans are the most common Latino group. Cook County's 925,000 Mexican Americans make up 17.5% of its population. Roughly 127,000 Puerto Ricans live in the county, while over 12,200 Cubans reside in the county. There are some 140,000 Hispanics and Latinos of other nationalities living in Cook County (i.e. Colombian, Bolivian, etc., and they collectively make up 2.6% of the county's population.


In 2010 statistics, the largest religious group in Cook County was the Archdiocese of Chicago, with 1,947,223 Catholics worshipping at 371 parishes, followed by 209,195 non-denominational adherents with 486 congregations, an estimated 201,152 Muslims with 62 congregations, 68,865 NBC Baptists with 99 congregations, 49,925 ELCA Lutherans with 145 congregations, 49,909 SBC Baptists with 181 congregations, 45,979 LCMS Lutherans with 120 congregations, 39,866 UCC Christians with 101 congregations, 33,584 UMC Methodists with 121 congregations, and 32,646 AG Pentecostals with 64 congregations. Altogether, 59.6% of the population was claimed as members by religious congregations, although members of historically African-American denominations were underrepresented due to incomplete information. In 2014, Cook County had 2,001 religious organizations, second only to Los Angeles County out of all US counties.





Unincorporated communities


The county is divided into 29 townships, in addition to the cities of Chicago and Evanston.

Worth Township Wheeling Township Thornton Township Stickney Township Stickney Township Schaumburg Township Riverside Township River Forest Township Rich Township Proviso Township Palos Township Palatine Township Orland Township Oak Park Township Norwood Park Township Northfield Township Niles Township New Trier Township Maine Township Lyons Township Leyden Township Lemont Township Hanover Township Evanston Elk Grove Township Cicero Township Calumet Township Bremen Township Bloom Township Berwyn Township Barrington TownshipMap of Cook County Illinois showing townships
Cook County townships (clickable)

Current townships

The 29 townships of Cook County, with their populations as of the 2010 Census, are:

  • Thornton Township – 169,326
  • Wheeling Township – 153,630
  • Worth Township – 152,633
  • Proviso Township – 151,704
  • Maine Township – 135,772
  • Schaumburg Township – 131,288
  • Palatine Township – 112,994
  • Lyons Township – 111,688
  • Bremen Township – 110,118
  • Niles Township – 105,882
  • Hanover Township – 99,538
  • Orland Township – 97,558
  • Elk Grove Township – 92,905
  • Leyden Township – 92,890
  • Bloom Township – 90,922
  • Northfield Township – 85,102
  • Cicero Township – 83,891
  • Rich Township – 76,727
  • Berwyn Township – 56,657
  • New Trier Township – 55,424
  • Palos Township – 54,615
  • Oak Park Township – 51,878
  • Stickney Township – 40,772
  • Norwood Park Township – 26,385
  • Lemont Township – 21,113
  • Calumet Township – 20,777
  • Barrington Township – 15,636
  • Riverside Township – 15,594
  • River Forest Township – 11,172

Former townships

Chicago's eight former townships and annexed parts of others no longer have any governmental structure or responsibility since their annexations, but their names and boundaries are still used on property plats and by Cook County for tax assessment purposes.

In 2014, Evanston Township was dissolved by voters and its functions were absorbed by the city of Evanston.

  • Evanston Township
  • Jefferson Township
  • Hyde Park Township
  • Lake Township
  • Lake View Township
  • North Township
  • Rogers Park Township
  • South Township
  • West Township



Construction of the Erie Canal in New York State made a connection from the Atlantic Ocean to the Great Lakes in 1821. As the Midwest farms proved productive, with much grain to sell to other parts of the US, Chicago and Cook County saw the benefit of a canal to improve the link from the Great Lakes to the Mississippi River. The Illinois and Michigan Canal was completed in 1848, extending from the Bridgeport neighborhood in Chicago on the Chicago River, to the Illinois River at the cities of LaSalle-Peru. This canal spurred the growth of Chicago and the areas around it, as water travel was the primary way to ship grain or other commodities in that part of the 19th century. The Illinois and Michigan Canal ceased major operation in 1933. Portions are now designated as a National Historic Corridor. The two canals and the Great Lakes cemented trade ties between the Midwest and the Northeast, encouraging farmers to grow more than they needed to feed themselves in Illinois, with a large market for grain now open to them. Towns in Cook County along the Canal grew. From a national perspective, the trade ties made the South region of the US less important to the Northeast as a trade partner.

The Chicago Sanitary and Ship Canal, completed in 1900, largely replaced the functions of the Illinois and Michigan Canal. This canal resulted in the reversal of the direction of flow of the main stem and the South branch of the Chicago River; they used to empty into Lake Michigan and now those river sections flow toward the Des Plaines River. The Sanitary and Ship Canal was built to serve many aims, including ending using Lake Michigan as a sewer, sending waste water through treatment plants and sending it away from Lake Michigan. It is also a waterway for movement of ships.

Railway network

The next major technology for transportation was railroads. Chicago and the towns along the canal and rivers understood the value of being a hub of a major network. Rail lines spurred out from Chicago by the 1850s, with major growth in the rail network for freight and passenger transportation coming after the Civil War, when the transcontinental railroads were completed, coast to coast across the US, stopping in Chicago, the heart of Cook County.

Major highways

Following on the well-established position of Chicago as a transportation hub, the Interstate highway network maintained Chicago as a hub of that network, as well as serving the travel needs within the region.

  • I-55
  • I-57
  • I-80
  • I-88
  • I-90 / I-94 / Chicago Skyway
  • I-190
  • I-290
  • I-294
  • I-355
  • US 6
  • US 12
  • US 14
  • US 20
  • US 30
  • US 34
  • US 41
  • US 45
  • US 66
  • Illinois 1.svg Illinois Route 1
  • Illinois 7.svg Illinois Route 7
  • Illinois 19.svg Illinois Route 19
  • Illinois 21.svg Illinois Route 21
  • Illinois 25.svg Illinois Route 25
  • Illinois 38.svg Illinois Route 38
  • Illinois 43.svg Illinois Route 43
  • Illinois 50.svg Illinois Route 50
  • Illinois 53.svg Illinois Route 53
  • Illinois 56.svg Illinois Route 56
  • Illinois 58.svg Illinois Route 58
  • Illinois 59.svg Illinois Route 59
  • Illinois 62.svg Illinois Route 62
  • Illinois 64.svg Illinois Route 64
  • Illinois 68.svg Illinois Route 68
  • Illinois 72.svg Illinois Route 72
  • Illinois 83.svg Illinois Route 83
  • Illinois 110.svg Illinois Route 110
  • Illinois 171.svg Illinois Route 171
  • Illinois 390.svg Illinois Route 390
  • Illinois 394.svg Illinois Route 394


When the age of air travel began in the 20th century, Midway Airport was built on one square mile of land and served as the major Chicago area airport from 1927 to 1955. Midway International Airport has been enlarged and continues to operate as of 2020. As air travel became more important for passenger travel, and then for select freight commodities, O'Hare International Airport was built adjacent to a military airfield in the northwest part of Cook County. The City of Chicago annexed the land for the airport, so that the city controls both airports serving a large area. During the second half of the 20th century, it was the world's busiest airport. The approach of Cook County and Chicago to air travel has been the same as the approach to canal, railroad and highway transportation, to serve as a major national hub.

There has been a long running plan for a third major airport to serve the south side of the city and the southern and southwestern suburbs, the Proposed Chicago south suburban airport intended for Peotone, Illinois. The state of Illinois has been addressing this topic since 1986. Some land has been acquired, but there is not a functioning airport there, as of August 2020.

Images for kids

See also

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