• county
  • FIPS 17131
  • Largest town: Aledo

Mercer County, Illinois

Mercer County had 15,292 residents in the Census Vintage 2024 estimate, on 561.2 square miles of land. It ranks 70th of 102 in Illinois by population and 45th by land area.

Population
15,292
#70 of 102 in Illinois · #2,073 in US
Area
561.2 sq mi
#45 of 102 in Illinois · #1,843 in US
Density
27 / sq mi
#78 of 102 in Illinois · #2,006 in US
Median household income
$77,098
#18 of 102 in Illinois · #576 in US

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

Mercer County within Illinois. Pin: Springfield.

Measure from here

Tools and pages that start from Mercer County

Mercer County population, land area and income

Mercer County had 15,292 residents in the Census Vintage 2024 estimate, on 561.2 square miles of land. It ranks 70th of 102 in Illinois by population and 45th by land area. That works out to 27.2 people per square mile, below the US average of 96.3, and below the national county median.

The median county-equivalent in Illinois has 24,447 residents; Mercer County is somewhat smaller.

Its SAIPE 2023 median household income of $77,098 is in the top quarter among 3,143 counties with an estimate.

National rank among 3,144

Population

15,292

3144th1st

2073rd of 3,144 (US)

Land area

561 sq mi

3144th1st

1843rd of 3,144 (US)

Density

27.2 / sq mi

3144th1st

2006th of 3,144 (US)

Median household income

$77,098

3143rd1st

576th of 3,143 (US)

Rank within Illinois (102)

Population

15,292

102nd1st

70th of 102 (IL)

Land area

561 sq mi

102nd1st

45th of 102 (IL)

Density

27.2 / sq mi

102nd1st

78th of 102 (IL)

Median household income

$77,098

102nd1st

18th of 102 (IL)

How Mercer County's population changed since 2020

Mercer County lost 340 residents between the July 2020 and July 2024 estimates, a drop of 2.2%. That ranks 61st 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, Mercer County recorded 567 births and 897 deaths, a natural change of -330. Net international migration added +6 and net domestic migration, people moving to or from other US counties, came to -70. The largest single component was natural change, which removed 330 people.

15.6k202015.6k202115.5k202215.5k202315.3k2024
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
567
Deaths
897
Net international migration
+6
Net domestic migration
-70
Change, July 2023 to July 2024
-164

Where Mercer County is

The Census internal point of Mercer County is at 41.205600, -90.741800. It sits in UTM zone 15N. The map shades Illinois's 102 county-equivalents by population change from 2020 to 2024, darker for faster growth, with Mercer 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: Mercer County internal point. Dark pin: Springfield.

Internal point

Decimal
41.205600, -90.741800
DMS
41°12'20.16"N 90°44'30.48"W
UTM
15N 689333.3E 4564039.6N
Geohash
9zr6rj7b4
Plus code
86HF6745+67

Towns in Mercer County

One incorporated place of 1,000+ people has residents in Mercer County, 3,522 people together, or 23% of the county. Each figure counts only the part of the town inside Mercer County; towns marked "part" extend into another county. The largest is Aledo with 3,522.

  1. 01Aledo3,522
Census Vintage 2024 subcounty estimates, county parts of incorporated places (SUMLEV 157).

Counties bordering Mercer County

The Census 2024 county adjacency file lists 7 neighbors for Mercer County, including 2 across a state line. The most populous is Rock Island County, IL, with 142,731 residents. Distances run between Census internal points in a straight line.

Distance to Springfield and the nearest big city

Springfield is 113.9 miles SSE of Mercer County's internal point in a straight line. The nearest place of 100,000 or more is Davenport, IA (population 100,938), 25.3 miles away. The nearest place of 10,000 or more is Rock Island, IL (population 36,434), 19.9 miles away.

Mercer County FIPS code

The FIPS code of Mercer County is 17131: state code 17 for Illinois plus county code 131. Use it as text, with the leading zero, when joining Census, BLS, or CDC county tables. SAIPE lists its 2023 median household income as $77,098.

Questions people ask

What is the population of Mercer County, Illinois?

The Census Vintage 2024 estimate for July 1, 2024 is 15,292. That is down 340 people (2.2%) from the July 2020 estimate of 15,632.

What is the FIPS code of Mercer County?

17131. The first two digits (17) are Illinois; the last three (131) identify the county.

What is the largest town in Mercer County?

Aledo, with 3,522 residents inside Mercer County in 2024.

Which counties border Mercer County?

7 county-equivalents border it in the Census 2024 adjacency file: Rock Island County, IL; Knox County, IL; Henry County, IL; Des Moines County, IA; Warren County, IL; Louisa County, IA; Henderson 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.