County outline
Where McDonough County is located
Area breakdown
Land accounts for 99.9% of McDonough County’s measured area and water for 0.1%. Its combined area converts to 1,528.4 square kilometers or approximately 377,664 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 589.305 | 1,526.293 | 377,155.2 |
| Water | 0.795 | 2.059 | 508.8 |
| Total | 590.1 | 1,528.352 | 377,664 |
How McDonough County compares
By original Census land area, McDonough County ranks #36 of 102 in Illinois and #1662 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 1.154 times the Illinois county-equivalent median of 510.7 square miles. It accounts for 1.1% of the combined county land area in the state.
See the complete Illinois ranking · What counts as a county equivalent?
Population and density of McDonough County
The Census Bureau estimates that 25,916 people lived in McDonough County on July 1, 2025. That ranks #1,634 of 3,222 county equivalents nationally and #51 of 102 in Illinois. Since the April 1, 2020 estimates base of 27,254, the population has declined by 1,338 (−4.9%), compared with −0.8% for Illinois as a whole.
With 589.3 square miles of land, that is 44 people per square mile (17 per km²), placing McDonough County #1,667 nationally for density and #53 in Illinois. The median county equivalent has 47 people per square mile; the Illinois median is 44. Put another way, there are about 15 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 27,128 | 27,122 | 26,777 | 26,804 | 26,115 | 25,916 |
| Change | — | −6 | −345 | +27 | −689 | −199 |
U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.
Cities and towns in McDonough County
11 incorporated places lie at least partly in McDonough County. Together they are home to 20,204 people (78%); the other 5,712 (22%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Macomb city, with 14,530 residents in the county.
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Macomb cityCounty seat | 14,530 | −5.8% | 10.8 |
| Bushnell city | 2,600 | −4.1% | 2.117 |
| Colchester city | 1,070 | −3.9% | 1.15 |
| Blandinsville village | 544 | −4.1% | 0.875 |
| Prairie City village | 392 | −3.7% | 1.008 |
| Industry village | 383 | −4% | 0.46 |
| Good Hope village | 349 | −3.6% | 0.3 |
| Bardolph village | 203 | −3.3% | 0.617 |
| Tennessee village | 98 | −2% | 0.425 |
| Sciota village | 32 | −3% | 0.312 |
| Plymouth villageAlso in 1 other county | 3 | 0% | 0.565 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside McDonough County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
McDonough County is a central county of the Macomb, IL Micropolitan Statistical Area. McDonough County is the area’s only county equivalent, so the micro area has the same 589.3 square miles of land. By combined land it ranks #362 of 542 micropolitan areas, and #471 by population.
ZIP codes
17 ZIP Code Tabulation Areas have land in McDonough County; 10 of them have most of their land inside the county, and the others mainly cover neighboring areas.
6141161416614206142261438614406145061452614556145961470614756148261484623266236762374
ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.
Counties bordering McDonough County
McDonough County shares a land border with 5 county equivalents. It has more land than 3 of them. The largest neighbor is Fulton County (865.7 mi²) and the smallest is Henderson County (378.8 mi²). Together with its neighbors, McDonough County forms a block of 3,607.2 mi² of land, of which it holds 16.3%.
| Bordering county equivalent | Land mi² | Size vs. McDonough | Compare |
|---|---|---|---|
| Fulton County | 865.7 | 1.5× larger | Compare |
| Hancock County | 793.7 | 1.3× larger | Compare |
| Warren County | 542.4 | 1.1× smaller | Compare |
| Schuyler County | 437.3 | 1.3× smaller | Compare |
| Henderson County | 378.8 | 1.6× smaller | Compare |
How big is McDonough County compared with U.S. states?
McDonough County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.8 times as much. Illinois’s county land could hold about 94 areas the size of McDonough County.
Another way to picture it: the same land area would fill a square about 24.3 miles (39.1 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.
State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.
What stands out about McDonough County?
McDonough County has more land than 1,560 of the other 3,221 county equivalents in the dataset.
A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.
Does including water change its rank?
Using land plus water places McDonough County at #1,782 nationally by total area, 120 places farther from the top than its land rank. Other county equivalents gain more area when their water measurements are included.
Its water share is 0.1%, compared with a national county-equivalent median of 1.2% — 1 percentage points lower. This describes the statistical geography’s land/water mix, not flood exposure or developable land.
Closest positions in the national land ranking
These entries sit immediately beside McDonough County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #1661 | Manitowoc County, Wisconsin | 589.3 | Compare |
| #1662 | McDonough County, Illinois | 589.3 | This county |
| #1663 | Simpson County, Mississippi | 589.2 | Compare |
Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.
Representative coordinates
The Census internal point is 40.455808, -90.678954. It represents a location inside the geography; it is not necessarily the centroid or the address of a courthouse.
Source and precision
U.S. Census Bureau, 2026 Gazetteer Files, Counties. Original ALAND: 1,526,291,850 m²; AWATER: 2,060,301 m². Rankings use ALAND; exact ties use ascending GEOID. Tables preserve Census-published square miles to three decimals, with conversions based on those values.
Common questions
How big is McDonough County?
McDonough County, Illinois has 589.3 square miles (1,526.3 km²) of land and 0.795 square miles of water, for a total area of 590.1 square miles. It ranks #1662 of 3,222 U.S. county equivalents by land area.
Is McDonough County the largest county in Illinois?
No. McDonough County ranks #36 of 102 in Illinois by land area. The largest is McLean County, with 1,183.2 square miles of land.
What counties border McDonough County?
McDonough County shares a land border with Fulton County, Hancock County, Schuyler County, Warren County, and Henderson County.
What is the population of McDonough County?
The Census Bureau estimates McDonough County had 25,916 residents on July 1, 2025, ranking #1,634 of 3,222 county equivalents. That is 44 people per square mile of land.
What is the county seat of McDonough County?
The county seat of McDonough County is Macomb.
What cities and towns are in McDonough County?
McDonough County has 11 incorporated places. The most populous five are Macomb city, Bushnell city, Colchester city, Blandinsville village, and Prairie City village; 5,712 residents live outside any incorporated place.
Is McDonough County part of a metropolitan area?
Yes. It is a central county of the Macomb, IL Micropolitan Statistical Area.
How many ZIP codes are in McDonough County?
17 ZIP Code Tabulation Areas have land in McDonough County, and 10 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does McDonough County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 1.8 times as much land.
How many acres of land are in McDonough County?
The land measurement converts to approximately 377,155 acres. Including water, total area is approximately 377,664 acres. One square mile equals 640 acres.
Why might another source show a different area?
Check whether it reports land or total area, its Census vintage, and its rounding. Our guide explains how to reconcile county area figures.
Can this establish a property boundary?
No. Statistical measurements and generalized maps do not establish property lines. Consult the relevant local surveying or land-records authority.