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Marion County, Illinois facts for kids

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Marion County
U.S. county
Marion County Courthouse in Salem
Marion County Courthouse in Salem
Flag of Marion County
Flag
Map of Illinois highlighting Marion County
Location within the U.S. state of Illinois
Map of the United States highlighting Illinois
Illinois's location within the U.S.
Country  United States
State  Illinois
Founded 1823
Named for Francis Marion
Seat Salem
Largest city Centralia
Area
 • Total 576 sq mi (1,490 km2)
 • Land 572 sq mi (1,480 km2)
 • Water 3.7 sq mi (10 km2)  0.6%
Population
 (2020)
 • Total 37,729
 • Estimate 
(2023)
 36,673 Decrease
 • Density 65.50/sq mi (25.290/km2)
Time zone UTC−6 (Central)
 • Summer (DST) UTC−5 (CDT)
Congressional district 15th

Marion County is a county located in the state of Illinois in the United States. In 2020, about 37,729 people lived here. The main town and county seat is Salem. Marion County is part of a larger area that includes Centralia and is connected to the bigger St. Louis area.

History of Marion County

Marion County was created on January 24, 1823. It was formed from parts of Jefferson and Fayette counties. The county was named after Revolutionary War General Francis Marion. He was known as the "Swamp Fox" because of his clever tactics.

  • Marion County Illinois 1823

    Marion County when it was first created in 1823

Geography of Marion County

Marion County covers a total area of 576 square miles. Most of this area, 572 square miles, is land. Only a small part, about 3.7 square miles, is water.

A special point in the county is where the Baseline meets the Third Principal Meridian. This spot is important because it was the starting point for surveying the Northwest Territory. You can find this marker south of Centralia, near U.S. 51.

Climate and Weather in Marion County

Weather chart for Salem, Illinois
J F M A M J J A S O N D
 
 
2.5
 
37
18
 
 
2.5
 
43
22
 
 
4
 
54
33
 
 
4
 
65
44
 
 
4.4
 
75
54
 
 
4.2
 
84
63
 
 
3.9
 
88
68
 
 
3.4
 
87
66
 
 
3.2
 
80
57
 
 
3.1
 
69
45
 
 
4.1
 
54
34
 
 
3.3
 
42
24
temperatures in °F
precipitation totals in inches
source: The Weather Channel
Metric conversion
J F M A M J J A S O N D
 
 
62
 
3
-8
 
 
64
 
6
-6
 
 
101
 
12
1
 
 
102
 
18
7
 
 
111
 
24
12
 
 
105
 
29
17
 
 
99
 
31
20
 
 
87
 
31
19
 
 
82
 
27
14
 
 
79
 
21
7
 
 
105
 
12
1
 
 
83
 
6
-4
temperatures in °C • precipitation totals in mm

In Salem, the county seat, temperatures change throughout the year. In January, the average low is 18°F. In July, the average high is 88°F. The coldest temperature ever recorded was -23°F in January 1994. The hottest was 105°F in August 1983.

The amount of rain also changes. January usually gets about 2.46 inches of rain. May is often the wettest month, with about 4.37 inches.

Transportation in Marion County

  • South Central Transit provides public transportation services.

Major Roads in Marion County

Several important highways pass through Marion County:

  • I-57.svg Interstate 57
  • US 50.svg U.S. Route 50
  • US 51.svg U.S. Route 51
  • Illinois 37.svg Illinois Route 37
  • Illinois 161.svg Illinois Route 161

Neighboring Counties

Marion County shares its borders with several other counties:

Population of Marion County

Historical population
Census Pop. %±
1830 2,125 —
1840 4,742 123.2%
1850 6,720 41.7%
1860 12,739 89.6%
1870 20,622 61.9%
1880 23,686 14.9%
1890 24,341 2.8%
1900 30,446 25.1%
1910 35,094 15.3%
1920 37,497 6.8%
1930 35,635 −5.0%
1940 47,989 34.7%
1950 41,700 −13.1%
1960 39,349 −5.6%
1970 38,986 −0.9%
1980 43,523 11.6%
1990 41,561 −4.5%
2000 41,691 0.3%
2010 39,437 −5.4%
2020 37,729 −4.3%
2023 (est.) 36,673 −7.0%
U.S. Decennial Census
1790-1960 1900-1990
1990-2000 2010

In 2010, there were 39,437 people living in Marion County. There were 16,148 households. About 30.9% of these households had children under 18 living with them. The average age of people in the county was 41.4 years old.

Communities in Marion County

Cities

Villages

Townships

Marion County is divided into seventeen smaller areas called townships:

  • Alma
  • Carrigan
  • Centralia
  • Foster
  • Haines
  • Iuka
  • Kinmundy
  • Meacham
  • Odin
  • Omega
  • Patoka
  • Raccoon
  • Romine
  • Salem
  • Sandoval
  • Stevenson
  • Tonti

Unincorporated Communities

These are smaller communities that are not officially part of a city or village:

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