What is the largest city in Williamson County, IL?

Marion is the largest city or town in Williamson County, with about 16,836 residents.

How many ZIP codes are in Williamson County?

Williamson County includes 11 ZIP Code Tabulation Areas, including 62841, 62915, 62918, 62921, 62922.

What is the population of Williamson County, IL?

About 66,876 people live in Williamson County, based on American Community Survey 5-year estimates.

What counties border Williamson County?

Williamson County borders Jackson County, Franklin County, Saline County, Union County, Johnson County.

Williamson County, IL: Cities, ZIP Codes & Local Data

Population

66,876

Land area

420sq mi

People per sq mi

159

ZIP codes

11

Williamson County at a glance

Williamson County is 30% less dense than Illinois as a whole.
Households here earn a median of $65,604 a year, 21% less than the Illinois figure of $83,390.
A typical owner-occupied home is valued at $156,400 (41% below Illinois) and median rent is $930 a month.
The biggest population centers are Marion (16,836), Herrin (12,226) and Carterville (5,818).

Local data for Williamson County, IL

Counts from official public data

Housing and community stats

Williamson County, IL, American Community Survey 2020-2024

Full profile

Median household income

$65,604

Poverty rate

13.8%

Median home value

$156,400

Prices +5.0% in a year

Median rent

$930/mo

Homeownership

70.7%

Bachelor's or higher

26.2%

Median age

41.6

Average commute

23.5 min

Largest reported origins and ancestries: German Americans (11,562), Irish Americans (9,099), Italian Americans (3,124).

Home values and rents Income, education and commute

Economy and federal money

Jobs, income, federal spending and pandemic loans

Details

Unemployment rate

3.6%

Sep 2026, -0.7 pts in a year

Average annual pay

$55,243

29,573 jobs, 2025

Income per person

$58,380

BEA, 2024

Federal spending

$629M

FY 2026, $9,373 per person

PPP loans

$122M

2,106 loans, 15,427 jobs reported

Campaign donations

$316K

Itemized, 2026 cycle

Economy Federal spending PPP loans

How people get to work

Williamson County, IL, workers 16 and older. American Community Survey 5-year estimates

Drove alone82.1%
Carpooled7.2%
Public transit0.3%
Walked0.5%
Bicycle0.1%
Taxi, ride-hailing, motorcycle or other1.0%
Worked from home8.8%

Average one-way commute: 23.5 minutes for people who do not work from home.

Environment and hazard risk

Williamson County, IL, from FEMA, NOAA and EPA

Full report

Natural hazard risk

Relatively Moderate

Top: strong wind

Storm events since 1996

849

Most often hail

Flood insurance policies

141

0.5% of homes, county

July high / Jan low

88° / 23°F

49.0 inches of rain a year

Hazards, floods and storm history Check a flood zone 4 historic places

Health statistics

Share of adults in Williamson County, IL, CDC PLACES estimates

All 40 measures

Obesity

40.1%

U.S. 33.3% +6.8 pts

Diabetes

12.4%

U.S. 12.1% about the same

Smoking

14.7%

U.S. 12.8% +1.9 pts

Uninsured (18-64)

7.5%

U.S. 11.1% -3.6 pts

Cities, towns and ZIP codes in Williamson County

Population shown

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Frequently asked questions

What is the largest city in Williamson County, IL?: Marion is the largest city or town in Williamson County, with about 16,836 residents.
How many ZIP codes are in Williamson County?: Williamson County includes 11 ZIP Code Tabulation Areas, including 62841, 62915, 62918, 62921, 62922.
What is the population of Williamson County, IL?: About 66,876 people live in Williamson County, based on American Community Survey 5-year estimates.
What counties border Williamson County?: Williamson County borders Jackson County, Franklin County, Saline County, Union County, Johnson County.