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Declo, Idaho
Location of Declo in Cassia County, Idaho.
Location of Declo in Cassia County, Idaho.
Declo, Idaho is located in the United States
Declo, Idaho
Declo, Idaho
Location in the United States
Country United States
State Idaho
County Cassia
 • Total 0.28 sq mi (0.72 km2)
 • Land 0.28 sq mi (0.72 km2)
 • Water 0.00 sq mi (0.00 km2)
4,219 ft (1,286 m)
 • Total 343
 • Estimate 
 • Density 1,332.13/sq mi (514.76/km2)
Time zone UTC-7 (Mountain (MST))
 • Summer (DST) UTC-6 (MDT)
ZIP code
Area code(s) 208
FIPS code 16-20980
GNIS feature ID 0397613

Declo is a city in Cassia County, Idaho, United States. It is part of the Burley, Idaho micropolitan area. The population was 343 at the time of the 2010 census, up from 338 in 2000.


The city was originally named Marshfield. In 1916, the name was changed to Declo. The name is an amalgam of the names of two resident families, Dethles and Cloughly.

The world's largest potato processing company was founded in 1923 near Declo by a 14-year-old entrepreneur named J.R. Simplot, who had moved to the area with his family as a toddler. The corporate headquarters for the J. R. Simplot Company are now located in Boise.


Declo is located at 42°31′10″N 113°37′48″W / 42.51944°N 113.63000°W / 42.51944; -113.63000 (42.519441, -113.629978), at an elevation of 4,219 feet (1,286 m) above sea level. According to the United States Census Bureau, the city has a total area of 0.28 square miles (0.73 km2), all of it land.


According to the Köppen Climate Classification system, Declo has a semi-arid climate, abbreviated "BSk" on climate maps.


Historical population
Census Pop.
1920 22
1930 196 790.9%
1940 238 21.4%
1950 219 −8.0%
1960 237 8.2%
1970 251 5.9%
1980 276 10.0%
1990 279 1.1%
2000 338 21.1%
2010 343 1.5%
2019 (est.) 369 7.6%
U.S. Decennial Census

2010 census

As of the census of 2010, there were 343 people, 115 households, and 87 families residing in the city. The population density was 1,225.0 inhabitants per square mile (473.0/km2). There were 127 housing units at an average density of 453.6 per square mile (175.1/km2). The racial makeup of the city was 85.1% White, 4.1% Native American, 9.9% from other races, and 0.9% from two or more races. Hispanic or Latino of any race were 15.2% of the population.

There were 115 households, of which 45.2% had children under the age of 18 living with them, 51.3% were married couples living together, 15.7% had a female householder with no husband present, 8.7% had a male householder with no wife present, and 24.3% were non-families. 21.7% of all households were made up of individuals, and 9.6% had someone living alone who was 65 years of age or older. The average household size was 2.98 and the average family size was 3.44.

The median age in the city was 29.8 years. 35.6% of residents were under the age of 18; 8.7% were between the ages of 18 and 24; 22.3% were from 25 to 44; 22.4% were from 45 to 64; and 10.8% were 65 years of age or older. The gender makeup of the city was 50.1% male and 49.9% female.


Declo is part of the Cassia County School District.

The following schools are located in Declo:

  • Declo Elementary School
  • Declo Junior High School
  • Declo High School

Notable people

  • J.R. Simplot, founder of the J. R. Simplot Company
  • Robert C. Moore, Western artist
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