Rock Island County area

Population and density of Rock Island County

The Census Bureau estimates that 141,869 people lived in Rock Island County on July 1, 2025. That ranks #481 of 3,222 county equivalents nationally and #15 of 102 in Illinois. Since the April 1, 2020 estimates base of 144,669, the population has declined by 2,800 (−1.9%), compared with −0.8% for Illinois as a whole.

With 427.5 square miles of land, that is 332 people per square mile (128 per km²), placing Rock Island County #470 nationally for density and #11 in Illinois. The median county equivalent has 47 people per square mile; the Illinois median is 44. Put another way, there are about 1.9 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 Rock Island County

15 incorporated places lie at least partly in Rock Island County. Together they are home to 125,054 people (88.1%); the other 16,815 (11.9%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Moline city, with 42,362 residents in the county. The county seat, Rock Island city, has 36,225 residents. By land, Rock Island city is the largest at 17.5 mi².

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

Metropolitan area

Rock Island County is a central county of the Davenport-Moline-Rock Island, IA-IL Metropolitan Statistical Area. Its 4 county equivalents have 380,452 residents on 2,270 square miles of land; Rock Island County accounts for 18.8% of the land and 37.3% of the residents. By combined land it ranks #143 of 393 metropolitan areas, and #149 by population. It belongs to the Davenport-Moline, IA-IL Combined Statistical Area.

ZIP codes

21 ZIP Code Tabulation Areas have land in Rock Island County; 17 of them have most of their land inside the county, and the others mainly cover neighboring areas.

612016123261236612376123961240612426124461256612576125961264612656127261273612756127861279612816128261284

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 Rock Island County

Rock Island County shares a land border with 6 county equivalents, including 3 in Iowa. Each of them has more land than Rock Island County. The largest neighbor is Henry County (823.2 mi²) and the smallest is Muscatine County (437.4 mi²). Together with its neighbors, Rock Island County forms a block of 4,086.5 mi² of land, of which it holds 10.5%.

How big is Rock Island County compared with U.S. states?

Rock Island County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2.4 times as much. Illinois’s county land could hold about 130 areas the size of Rock Island County.

Another way to picture it: the same land area would fill a square about 20.7 miles (33.3 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 Rock Island County?

Rock Island County has more land than 846 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 Rock Island County at #2,342 nationally by total area, 34 places closer to the top than its land rank. The water assigned to this geography moves it ahead of some county equivalents with more land.

Its water share is 5.3%, compared with a national county-equivalent median of 1.2% — 4.1 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 Rock Island 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.