Williamson County, Illinois Population 2026
Updated April 2026 · US Census ACS 2023 5-Year Estimates · 22nd-largest in Illinois
The population of Williamson County, Illinois is 66,902 as of the 2023 American Community Survey, making it the 22nd-largest county in Illinois. The median household income is $65,521, the median home value is $145,600, and the median age is 41.4.
The population of Williamson County has grown 0.9% since 2010 (66,440 → 67,064), a +0.07% annualized rate.
66,902
Population
+0.07%
Annual growth
159
People / sq mi
$65,521
Median Income
$145,600
Median Home Value
Williamson County covers 420 sq mi of land at 159.2 people per square mile.
About Williamson County, IL
What distinguishes Williamson County is density: among the most densely settled of US counties, around 159 people per square mile. Williamson County is a county in Illinois with a population of 66,902. It ranks #22 among counties in Illinois by population.
The typical household here earns about $65,521, below the US median of $78,538. About 10.1% of residents live below the federal poverty level, below the national 12.4%. The typical home is valued at $145,600, with typical rent around $897.
Educational attainment is on the higher side for US counties — 27.5% of adults hold a four-year degree, below the national 35.0%. About 8.6% of the workforce is home-based, below the national 14.0%, and the average commute runs about 23 minutes each way.
That density explains much of the rest of the profile in Williamson County: denser places lean toward renting, shorter commutes by transit, and a younger working-age mix.
Williamson County Population History (2010-2024)
The county of Williamson County had a population of 66,440 in 2010 and 67,064 in 2024, a 0.9% growth over 14 years. The peak was 67,504 in 2016. Average annual growth rate: 0.07%.
67,064
Population (2024)
66,440
Population (2010)
67,504
Peak (2016)
0.07%
Avg Annual Growth
| Year | Population |
|---|---|
| 2010 | 66,440 |
| 2011 | 66,745 |
| 2012 | 66,793 |
| 2013 | 67,472 |
| 2014 | 67,439 |
| 2015 | 67,457 |
| 2016 | 67,504 |
| 2017 | 67,076 |
| 2018 | 67,017 |
| 2019 | 66,633 |
| 2020 | 67,121 |
| 2021 | 66,895 |
| 2022 | 66,565 |
| 2023 | 66,737 |
| 2024 | 67,064 |
Race & Ethnicity
| White | 89.2% |
| Black or African American | 3.5% |
| Asian | 0.1% |
| Hispanic or Latino (any race) | 2.1% |
| Two or More Races | 0.0% |
Age & Sex
41.4
Median Age
49.7%
Female
50.3%
Male
19.6%
Age 65+
Age Distribution
Children (under 15): 17.8% · Seniors (65+): 19.6%
Income & Poverty
| Median household income | $65,521$-16,181 vs state |
| Mean household income | $85,557 |
| Per-capita income | $37,096 |
| Poverty rate | 10.1%+1.9% vs state |
| Unemployment rate | 2.5% |
| Employment-to-population | 55.5% |
Top Industries by Employment
The largest employment sector in Williamson County is professional & business services, accounting for 30.8% of workers.
How residents commute
0.3%
Drive alone
0.8%
Carpool
81.5%
Public transit
8.6%
Work from home
23.2 min
Avg commute
Housing
$145,600$-104,900 vs state
Median home value
$897
Median rent
71.1%
Homeownership rate
31,957
Total housing units
90.0%
Occupied
10.0%
Vacant
28.9%
Renter-occupied
Social & access
94.8%
With health insurance
92.1%
With broadband internet
21.1%
Foreign-born
8.7%
Veterans (18+)
19.0%
With a disability
96.5%
Speak language other than English at home
Education
92.4%
High School+
27.5%
Bachelor's+
Largest cities in Illinois
Other counties in Illinois
Part of Illinois
Metro areas in Illinois
County rankings
Frequently Asked Questions
Williamson County, Illinois has a population of 66,902 according to the US Census Bureau's 2023 American Community Survey 5-year estimates, making it the 22nd-largest county in Illinois. Population density is 159 people per square mile.
The population of Williamson County has grown 0.9% since 2010 (66,440 → 67,064), a +0.07% annualized rate.
The median household income in Williamson County, Illinois is $65,521, with mean (average) household income of $85,557 and per-capita income of $37,096. 10.1% of residents live below the federal poverty level.
In Williamson County, the largest racial and ethnic groups are White (89.2%), Black or African American (3.5%), Hispanic or Latino (2.1%). Figures are from the US Census Bureau's 2023 ACS 5-year estimates and reflect self-reported responses.
The median age in Williamson County, Illinois is 41.4 years. Residents are 49.7% female and 50.3% male.
The median home value in Williamson County is $145,600 and median monthly rent is $897. 71.1% of occupied housing units are owner-occupied. The county has 31,957 total housing units, 10.0% of which are vacant.
The largest employment sector in Williamson County, Illinois is professional, scientific, and management services, employing 30.8% of workers. The unemployment rate is 2.5%.
Chicago is among the largest cities associated with Williamson County, Illinois, with a population of 2,707,648.
Williamson County, IL Climate
Williamson County, IL has an average annual temperature of 13.4°C (56°F) and receives about 1152 mm of precipitation per year. The warmest month is July and the coldest is January. Figures are 1970–2000 climate normals.
13.4°C
Avg Temp
1152
Precip (mm/yr)
Jul
Hottest Month
Jan
Coldest Month
| Month | Avg (°C/°F) | Precip |
|---|---|---|
| January | 0° / 31° | 74 mm |
| February | 2° / 36° | 79 mm |
| March | 8° / 46° | 121 mm |
| April | 14° / 56° | 110 mm |
| May | 19° / 65° | 121 mm |
| June | 23° / 74° | 102 mm |
| July | 26° / 78° | 94 mm |
| August | 25° / 76° | 90 mm |
| September | 21° / 70° | 79 mm |
| October | 14° / 58° | 75 mm |
| November | 8° / 47° | 106 mm |
| December | 2° / 36° | 101 mm |
1970–2000 normals from WorldClim 2.1 (~9 km grid). Precipitation can be less precise near mountains or coastlines, where rainfall varies sharply over short distances.
Best time to visit Williamson County, IL
The most comfortable months to visit Williamson County, IL are typically September, June and August, when temperatures are mildest and rainfall is relatively low. The hottest month is July (around 32°C high). The coldest is January (near -5°C low). March is usually the wettest month.
Where to stay near Williamson County
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Data from the American Community Survey (ACS) 5-Year estimates.
Source: U.S. Census Bureau ACS, 2026.