Boone County area

Population and density of Boone County

The Census Bureau estimates that 53,568 people lived in Boone County on July 1, 2025. That ranks #981 of 3,222 county equivalents nationally and #26 of 102 in Illinois. Since the April 1, 2020 estimates base of 53,446, the population has grown by 122 (+0.2%), compared with −0.8% for Illinois as a whole.

With 280.7 square miles of land, that is 191 people per square mile (74 per km²), placing Boone County #657 nationally for density and #16 in Illinois. The median county equivalent has 47 people per square mile; the Illinois median is 44. Put another way, there are about 3.4 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 Boone County

7 incorporated places lie at least partly in Boone County. Together they are home to 35,132 people (65.6%); the other 18,436 (34.4%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Belvidere city, with 25,462 residents in the county. By land, Loves Park city is the largest at 16.3 mi² across all its counties. Among places with at least 1,000 residents in 2020, Poplar Grove village grew fastest since then (+2.9%).

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

Metropolitan area

Boone County is a central county of the Rockford, IL Metropolitan Statistical Area. Its 2 county equivalents have 337,242 residents on 793.8 square miles of land; Boone County accounts for 35.4% of the land and 15.9% of the residents. By combined land it ranks #306 of 393 metropolitan areas, and #161 by population. It belongs to the Rockford-Freeport-Rochelle, IL Combined Statistical Area.

ZIP codes

15 ZIP Code Tabulation Areas have land in Boone County; 5 of them have most of their land inside the county, and the others mainly cover neighboring areas.

600336013560145601466100861011610126101661038610656107361080611076111161114

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 Boone County

Boone County shares a land border with 5 county equivalents, including 2 in Wisconsin. Each of them has more land than Boone County. The largest neighbor is Rock County (718.2 mi²) and the smallest is Winnebago County (513 mi²). Together with its neighbors, Boone County forms a block of 3,302.1 mi² of land, of which it holds 8.5%.

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

Boone County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 3.7 times as much. Illinois’s county land could hold about 198 areas the size of Boone County.

Another way to picture it: the same land area would fill a square about 16.8 miles (27 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 Boone County?

Boone County has more land than 376 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 Boone County at #2,887 nationally by total area, 41 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 0.5%, compared with a national county-equivalent median of 1.2% — 0.7 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 Boone 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.