Marion County is a county located in the U.S. state of Illinois. According to the 2020 census, it had a population of 37,729.^[1] Its county seat is Salem.^[2]

Quick Facts Country, State ...

Marion County
County
Marion County Courthouse in Salem
Flag
Location within the U.S. state of Illinois
Illinois's location within the U.S.
Coordinates: 38°39′N 88°55′W
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
• Density	66/sq mi (25/km2)
Time zone	UTC−6 (Central)
• Summer (DST)	UTC−5 (CDT)
Congressional district	15th

Close

Marion County comprises the Centralia, IL Micropolitan Statistical Area, which is included in the St. Louis-St. Charles-Farmington, MO-IL Combined Statistical Area.

Marion County was organized on January 24, 1823, from portions of Jefferson and Fayette counties. It was named in honor of Revolutionary War Gen. Francis Marion, the "Swamp Fox".^[3]

• Marion County at the time of its creation in 1823

According to the U.S. Census Bureau, the county has a total area of 576 square miles (1,490 km²), of which 572 square miles (1,480 km²) is land and 3.7 square miles (9.6 km²) (0.6%) is water.^[4]

The southwest corner of Marion County is the intersection of the Baseline with the Third Principal Meridian, the point of origin for the third survey of the Northwest Territory under the Land Ordinance of 1785. The origin is marked with a boulder south of Centralia just off U.S. 51.

As of the 2010 United States Census, there were 39,437 people, 16,148 households, and 10,746 families residing in the county.^[12] The population density was 68.9 inhabitants per square mile (26.6/km²). There were 18,296 housing units at an average density of 32.0 per square mile (12.4/km²).^[4] The racial makeup of the county was 93.1% white, 3.9% black or African American, 0.6% Asian, 0.3% American Indian, 0.4% from other races, and 1.6% from two or more races. Those of Hispanic or Latino origin made up 1.4% of the population.^[12] In terms of ancestry, 27.5% were German, 15.8% were Irish, 13.6% were English, and 10.8% were American.^[13]

Of the 16,148 households, 30.9% had children under the age of 18 living with them, 48.9% were married couples living together, 12.8% had a female householder with no husband present, 33.5% were non-families, and 28.8% of all households were made up of individuals. The average household size was 2.40 and the average family size was 2.91. The median age was 41.4 years.^[12]

The median income for a household in the county was $38,974 and the median income for a family was $50,518. Males had a median income of $41,428 versus $28,042 for females. The per capita income for the county was $20,493. About 12.2% of families and 16.5% of the population were below the poverty line, including 23.9% of those under age 18 and 9.6% of those age 65 or over.^[14]

Initially a strongly Democratic anti-Yankee county, Marion County has undergone two transitions. Between 1912 and 2004 it was a perfect bellwether apart from the Catholicism-influenced 1960 election when substantial anti-Catholic voting by its largely southern white population caused it to support Republican Richard Nixon. Since the beginning of the twenty-first century it has voted consistently for Republican presidential candidates.

• National Register of Historic Places listings in Marion County, Illinois