Adams County area

Population and density of Adams County

The Census Bureau estimates that 64,267 people lived in Adams County on July 1, 2025. That ranks #862 of 3,222 county equivalents nationally and #23 of 102 in Illinois. Since the April 1, 2020 estimates base of 65,745, the population has declined by 1,478 (−2.2%), compared with −0.8% for Illinois as a whole.

With 855.2 square miles of land, that is 75 people per square mile (29 per km²), placing Adams County #1,209 nationally for density and #32 in Illinois. The median county equivalent has 47 people per square mile; the Illinois median is 44. Put another way, there are about 8.5 acres of land per resident.

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 Adams County

14 incorporated places lie at least partly in Adams County. Together they are home to 45,246 people (70.4%); the other 19,021 (29.6%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Quincy city, with 38,918 residents in the county.

Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Adams County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.

Metropolitan area

Adams County is a central county of the Quincy, IL-MO Micropolitan Statistical Area. Its 2 county equivalents have 74,146 residents on 1,360.2 square miles of land; Adams County accounts for 62.9% of the land and 86.7% of the residents. By combined land it ranks #126 of 542 micropolitan areas, and #90 by population. It belongs to the Quincy-Hannibal, IL-MO Combined Statistical Area.

ZIP codes

23 ZIP Code Tabulation Areas have land in Adams County; 16 of them have most of their land inside the county, and the others mainly cover neighboring areas.

6230162305623116231262314623166232062324623256233862339623436234662347623486234962351623596236062365623736237662379

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 Adams County

Adams County shares a land border with 6 county equivalents, including 2 in Missouri. It has more land than every one of them. The largest neighbor is Pike County (831.4 mi²) and the smallest is Brown County (305.7 mi²). Together with its neighbors, Adams County forms a block of 4,165.2 mi² of land, of which it holds 20.5%.

How big is Adams County compared with U.S. states?

Adams County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.2 times as much. Illinois’s county land could hold about 65 areas the size of Adams County.

Another way to picture it: the same land area would fill a square about 29.2 miles (47.1 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 Adams County?

Adams County has more land than 2,247 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 Adams County at #1,042 nationally by total area, 67 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 1.9%, compared with a national county-equivalent median of 1.2% — 0.7 percentage points higher. 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 Adams County in the national ranking. They can be in different states and are not necessarily geographic neighbors.

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.