| County: | Marion County |
| State: | Illinois |
| Flag: | Flag of Marion County, Illinois.png |
| Founded: | 1823 |
| Seat Wl: | Salem |
| Largest City Wl: | Centralia |
| Area Total Sq Mi: | 576 |
| Area Land Sq Mi: | 572 |
| Area Water Sq Mi: | 3.7 |
| Area Percentage: | 0.6 |
| Population As Of: | 2020 |
| Population Total: | 37729 |
| Population Density Sq Mi: | auto |
| Time Zone: | Central |
| Ex Image: | Marion County Courthouse in Salem.jpg |
| District: | 15th |
| Named For: | Francis Marion |
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]
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]
According to the U.S. Census Bureau, the county has a total area of, of which is land and (0.6%) is water.
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.
In recent years, average temperatures in the county seat of Salem have ranged from a low of in January to a high of in July, although a record low of was recorded in January 1994 and a record high of was recorded in August 1983. Average monthly precipitation ranged from in January to in May.
As of the 2010 United States Census, there were 39,437 people, 16,148 households, and 10,746 families residing in the county.[4] The population density was . There were 18,296 housing units at an average density of .[5] 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.[4] In terms of ancestry, 27.5% were German, 15.8% were Irish, 13.6% were English, and 10.8% were American.[6]
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.[4]
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.[7]
Marion County is divided into seventeen townships:
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.