• county
  • FIPS 17163
  • Largest town: Belleville

St. Clair County, Illinois

St. Clair County had 251,149 residents in the Census Vintage 2024 estimate, on 657.8 square miles of land. It ranks 9th of 102 in Illinois by population and 28th by land area.

Population
251,149
#9 of 102 in Illinois · #292 in US
Area
657.8 sq mi
#28 of 102 in Illinois · #1,428 in US
Density
382 / sq mi
#9 of 102 in Illinois · #356 in US
Median household income
$66,007
#51 of 102 in Illinois · #1,296 in US

Census Vintage 2024 estimates · SAIPE 2023 income · 2024 Gazetteer land area

St. Clair County within Illinois. Pin: Springfield.

Measure from here

Tools and pages that start from St. Clair County

St. Clair County population, land area and income

St. Clair County had 251,149 residents in the Census Vintage 2024 estimate, on 657.8 square miles of land. It ranks 9th of 102 in Illinois by population and 28th by land area. That works out to 381.8 people per square mile, 4.0 times the US average of 96.3, and in the top quarter nationally.

The median county-equivalent in Illinois has 24,447 residents, so St. Clair County is 10.3 times that size.

Its SAIPE 2023 median household income of $66,007 is above the national county median among 3,143 counties with an estimate.

National rank among 3,144

Population

251,149

3144th1st

292nd of 3,144 (US)

Land area

658 sq mi

3144th1st

1428th of 3,144 (US)

Density

381.8 / sq mi

3144th1st

356th of 3,144 (US)

Median household income

$66,007

3143rd1st

1296th of 3,143 (US)

Rank within Illinois (102)

Population

251,149

102nd1st

9th of 102 (IL)

Land area

658 sq mi

102nd1st

28th of 102 (IL)

Density

381.8 / sq mi

102nd1st

9th of 102 (IL)

Median household income

$66,007

102nd1st

51st of 102 (IL)

How St. Clair County's population changed since 2020

St. Clair County lost 5,921 residents between the July 2020 and July 2024 estimates, a drop of 2.3%. That ranks 67th of 102 in Illinois for growth. The median Illinois county changed by -1.7%, and the state as a whole by -0.7%.

Since the April 2020 estimates base, St. Clair County recorded 10,713 births and 12,531 deaths, a natural change of -1,818. Net international migration added +1,475 and net domestic migration, people moving to or from other US counties, came to -6,196. The largest single component was domestic migration, which removed 6,196 people.

257.1k2020255.2k2021252.9k2022252.1k2023251.1k2024
Census Vintage 2024 county estimates for July 1 of each year. The axis starts above zero so year-to-year changes are visible.

Components of change, April 2020 to July 2024

Births
10,713
Deaths
12,531
Net international migration
+1,475
Net domestic migration
-6,196
Change, July 2023 to July 2024
-945

Where St. Clair County is

The Census internal point of St. Clair County is at 38.470200, -89.928500. It sits in UTM zone 16N. The map shades Illinois's 102 county-equivalents by population change from 2020 to 2024, darker for faster growth, with St. Clair County outlined. Dots are towns of 1,000+ people with residents in it.

Piatt County: -0.3%Hamilton County: -2.2%Williamson County: -0.1%Edgar County: -2.4%Macoupin County: -2.3%Marshall County: -1.3%Putnam County: +0.0%Richland County: -2.8%Washington County: -1.4%Lee County: -1.5%Douglas County: +0.2%Cook County: -1.6%Effingham County: -0.3%Edwards County: -3.6%Cass County: -2.0%Clay County: -3.4%Knox County: -2.2%LaSalle County: -0.9%Cumberland County: -1.3%Warren County: -3.7%Moultrie County: -0.9%Menard County: -2.5%Fayette County: -1.5%Boone County: -0.0%Lawrence County: -3.2%Marion County: -3.2%Champaign County: +3.0%Clark County: -2.4%Ford County: -0.4%Wayne County: -1.4%Logan County: -1.4%Grundy County: +2.5%Jasper County: -1.8%Crawford County: -1.3%McDonough County: -1.7%Clinton County: +0.5%Perry County: -3.0%Montgomery County: -2.2%Henry County: -2.0%Livingston County: -1.2%Scott County: -3.8%Alexander County: -11.2%Bureau County: -2.2%Brown County: +1.1%Mason County: -3.9%Calhoun County: -4.1%Greene County: -4.3%Coles County: -1.4%Kendall County: +8.2%Lake County: +0.7%Mercer County: -2.2%St. Clair County: -2.3%Wabash County: -3.0%Bond County: -1.7%DuPage County: +0.6%Gallatin County: -5.2%Stephenson County: -3.3%McHenry County: +1.9%White County: -3.0%Saline County: -3.9%Christian County: -2.2%Sangamon County: -1.0%Massac County: -3.6%Macon County: -2.9%Johnson County: -0.0%Jo Daviess County: -2.6%Peoria County: -1.0%DeKalb County: +1.0%Pope County: -1.5%De Witt County: -0.9%Schuyler County: -1.7%Fulton County: -3.1%Ogle County: -0.8%Jersey County: -1.6%Iroquois County: -3.3%Kankakee County: -0.9%Rock Island County: -1.1%Pulaski County: -5.8%Kane County: +0.9%Union County: -2.4%Whiteside County: -1.7%Woodford County: -0.3%Carroll County: -1.5%Adams County: -2.3%Hardin County: -2.6%Madison County: -1.0%Hancock County: -3.1%Monroe County: +0.0%Tazewell County: -1.1%Jackson County: -0.1%Vermilion County: -3.9%Randolph County: -0.6%McLean County: +0.5%Morgan County: -2.6%Shelby County: -1.7%Will County: +1.7%Winnebago County: -0.4%Jefferson County: -2.4%Stark County: -2.2%Henderson County: -4.5%Pike County: -2.6%Franklin County: -1.8%
Change 2020 to 2024
  1. < -3.0%
  2. < -2.2%
  3. < -1.4%
  4. < -0.3%
  5. ≥ -0.3%
no data

Orange pin: St. Clair County internal point. Dark pin: Springfield.

Internal point

Decimal
38.470200, -89.928500
DMS
38°28'12.72"N 89°55'42.60"W
UTM
16N 244510.5E 4262050.7N
Geohash
dnb4cek14
Plus code
86CGF3CC+3J

Towns in St. Clair County

22 incorporated places of 1,000+ people have residents in St. Clair County, 198,426 people together, or 79% of the county. Each figure counts only the part of the town inside St. Clair County; towns marked "part" extend into another county. The largest is Belleville with 40,560.

  1. 01Belleville40,560
  2. 02O'Fallon32,169
  3. 03East St. Louis17,808
  4. 04Cahokia Heights17,052
  5. 05Fairview Heights16,115
  6. 06Shiloh14,754
  7. 07Swansea14,445
  8. 08Mascoutah9,118
  9. 09Lebanon4,628
  10. 10Freeburg4,518
  11. 11Caseyville4,395
  12. 12Millstadt3,957
  13. 13Smithton3,888
  14. 14Dupo3,797
  15. 15Collinsville (part)2,578
Census Vintage 2024 subcounty estimates, county parts of incorporated places (SUMLEV 157).

Counties bordering St. Clair County

The Census 2024 county adjacency file lists 7 neighbors for St. Clair County, including 2 across a state line. The most populous is St. Louis County, MO, with 992,929 residents. Distances run between Census internal points in a straight line.

Distance to Springfield and the nearest big city

Springfield is 91.8 miles N of St. Clair County's internal point in a straight line. The nearest place of 100,000 or more is St. Louis, MO (population 279,695), 20.6 miles away. The nearest place of 10,000 or more is Belleville, IL (population 40,560), 4.6 miles away.

St. Clair County FIPS code

The FIPS code of St. Clair County is 17163: state code 17 for Illinois plus county code 163. Use it as text, with the leading zero, when joining Census, BLS, or CDC county tables. SAIPE lists its 2023 median household income as $66,007.

Questions people ask

What is the population of St. Clair County, Illinois?

The Census Vintage 2024 estimate for July 1, 2024 is 251,149. That is down 5,921 people (2.3%) from the July 2020 estimate of 257,070.

What is the FIPS code of St. Clair County?

17163. The first two digits (17) are Illinois; the last three (163) identify the county.

What is the largest town in St. Clair County?

Belleville, with 40,560 residents inside St. Clair County in 2024.

Which counties border St. Clair County?

7 county-equivalents border it in the Census 2024 adjacency file: St. Louis County, MO; St. Louis city, MO; Madison County, IL; Clinton County, IL; Monroe County, IL; Randolph County, IL; Washington County, IL.

Sources and data as of

Data as of: Census Vintage 2024 population estimates, 2024 Gazetteer land area and internal points, SAIPE 2023 median household income.

  1. 01Census Vintage 2024 county population estimates
  2. 02Census 2024 Gazetteer, counties
  3. 03Census SAIPE 2023 state and county estimates
  4. 04Census Vintage 2024 subcounty population estimates
  5. 05Census 2024 county adjacency file
  6. 06Census 2024 cartographic boundary file, counties (1:5,000,000)

How every number is computed: methodology. Spotted a wrong figure? Report an error.