Putnam County area

Population and density of Putnam County

The Census Bureau estimates that 5,619 people lived in Putnam County on July 1, 2025. That ranks #2,841 of 3,222 county equivalents nationally and #94 of 102 in Illinois. Since the April 1, 2020 estimates base of 5,631, the population has declined by 12 (−0.2%), compared with −0.8% for Illinois as a whole.

With 160.1 square miles of land, that is 35 people per square mile (14 per km²), placing Putnam County #1,873 nationally for density and #67 in Illinois. The median county equivalent has 47 people per square mile; the Illinois median is 44. Put another way, there are about 18 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 Putnam County

6 incorporated places lie at least partly in Putnam County. Together they are home to 3,327 people (59.2%); the other 2,292 (40.8%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Granville village, with 1,325 residents in the county. The county seat, Hennepin village, has 747 residents. By land, Hennepin village is the largest at 5.307 mi².

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

Metropolitan area

Putnam County is an outlying county of the Ottawa, IL Micropolitan Statistical Area. Its 3 county equivalents have 145,902 residents on 2,164.3 square miles of land; Putnam County accounts for 7.4% of the land and 3.9% of the residents. By combined land it ranks #73 of 542 micropolitan areas, and #9 by population. It belongs to the Chicago-Naperville, IL-IN-WI Combined Statistical Area.

ZIP codes

8 ZIP Code Tabulation Areas have land in Putnam County; 7 of them have most of their land inside the county, and the others mainly cover neighboring areas.

6132661327613346133561336613406136361560

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 Putnam County

Putnam County shares a land border with 3 county equivalents. Each of them has more land than Putnam County. The largest neighbor is LaSalle County (1,135.1 mi²) and the smallest is Marshall County (386.8 mi²). Together with its neighbors, Putnam County forms a block of 2,551.1 mi² of land, of which it holds 6.3%.

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

Putnam County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 6.5 times as much. Illinois’s county land could hold about 347 areas the size of Putnam County.

Another way to picture it: the same land area would fill a square about 12.7 miles (20.4 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 Putnam County?

Putnam County has more land than 170 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 Putnam County at #3,061 nationally by total area, 9 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 7%, compared with a national county-equivalent median of 1.2% — 5.8 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 Putnam 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.