County outline
Where Riley County is located
Area breakdown
Land accounts for 98% of Riley County’s measured area and water for 2%. Its combined area converts to 1,611.1 square kilometers or approximately 398,113 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 609.66 | 1,579.012 | 390,182.4 |
| Water | 12.391 | 32.093 | 7,930.2 |
| Total | 622.051 | 1,611.105 | 398,112.6 |
How Riley County compares
By original Census land area, Riley County ranks #82 of 105 in Kansas and #1588 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.835 times the Kansas county-equivalent median of 729.7 square miles. It accounts for 0.7% of the combined county land area in the state.
See the complete Kansas ranking · What counts as a county equivalent?
Population and density of Riley County
The Census Bureau estimates that 72,598 people lived in Riley County on July 1, 2025. That ranks #776 of 3,222 county equivalents nationally and #7 of 105 in Kansas. Since the April 1, 2020 estimates base of 71,962, the population has grown by 636 (+0.9%), compared with +1.3% for Kansas as a whole.
With 609.7 square miles of land, that is 119 people per square mile (46 per km²), placing Riley County #876 nationally for density and #7 in Kansas. The median county equivalent has 47 people per square mile; the Kansas median is 8.1. Put another way, there are about 5.4 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 72,011 | 71,889 | 71,587 | 71,530 | 72,072 | 72,598 |
| Change | — | −122 | −302 | −57 | +542 | +526 |
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 Riley County
5 incorporated places lie at least partly in Riley County. Together they are home to 57,884 people (79.7%); the other 14,714 (20.3%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Manhattan city, with 54,672 residents in the county (the city extends into 1 other county). Among places with at least 1,000 residents in 2020, Manhattan city grew fastest since then (+1.1%).
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Manhattan cityCounty seat · Also in 1 other county | 54,672 | +1.1% | 20.4 |
| Ogden city | 1,655 | −0.7% | 1.673 |
| Riley city | 956 | +1.6% | 0.508 |
| Leonardville city | 442 | +2.6% | 0.306 |
| Randolph city | 159 | −0.6% | 0.275 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Riley County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Riley County is a central county of the Manhattan, KS Metropolitan Statistical Area. Its 3 county equivalents have 136,122 residents on 1,835 square miles of land; Riley County accounts for 33.2% of the land and 53.3% of the residents. By combined land it ranks #171 of 393 metropolitan areas, and #311 by population.
| County equivalent | Population 2025 | Land mi² |
|---|---|---|
| Riley County | 72,598 | 609.7 |
| Geary County | 36,338 | 384.7 |
| Pottawatomie County | 27,186 | 840.7 |
ZIP codes
14 ZIP Code Tabulation Areas have land in Riley County; 8 of them have most of their land inside the county, and the others mainly cover neighboring areas.
6641166441664426644966502665036650666517665316654866554669336743267447
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 Riley County
Riley County shares a land border with 6 county equivalents. It has more land than 1 of them. The largest neighbor is Marshall County (900.2 mi²) and the smallest is Geary County (384.7 mi²). Together with its neighbors, Riley County forms a block of 5,069.6 mi² of land, of which it holds 12%.
| Bordering county equivalent | Land mi² | Size vs. Riley | Compare |
|---|---|---|---|
| Marshall County | 900.2 | 1.5× larger | Compare |
| Washington County | 894.8 | 1.5× larger | Compare |
| Pottawatomie County | 840.7 | 1.4× larger | Compare |
| Wabaunsee County | 794.3 | 1.3× larger | Compare |
| Clay County | 645.3 | 1.1× larger | Compare |
| Geary County | 384.7 | 1.6× smaller | Compare |
How big is Riley County compared with U.S. states?
Riley County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.7 times as much. Kansas’s county land could hold about 134 areas the size of Riley County.
Another way to picture it: the same land area would fill a square about 24.7 miles (39.7 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 Riley County?
Riley County has more land than 1,634 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 Riley County at #1,664 nationally by total area, 76 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 2%, compared with a national county-equivalent median of 1.2% — 0.8 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 Riley County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #1587 | Ouachita Parish, Louisiana | 610.1 | Compare |
| #1588 | Riley County, Kansas | 609.7 | This county |
| #1589 | Scott County, Mississippi | 609.2 | 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 39.291210, -96.727488. 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: 1,579,010,814 m²; AWATER: 32,092,077 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 Riley County?
Riley County, Kansas has 609.7 square miles (1,579 km²) of land and 12.4 square miles of water, for a total area of 622.1 square miles. It ranks #1588 of 3,222 U.S. county equivalents by land area.
Is Riley County the largest county in Kansas?
No. Riley County ranks #82 of 105 in Kansas by land area. The largest is Butler County, with 1,429.7 square miles of land.
What counties border Riley County?
Riley County shares a land border with Pottawatomie County, Geary County, Clay County, Wabaunsee County, Marshall County, and Washington County.
What is the population of Riley County?
The Census Bureau estimates Riley County had 72,598 residents on July 1, 2025, ranking #776 of 3,222 county equivalents. That is 119 people per square mile of land.
What is the county seat of Riley County?
The county seat of Riley County is Manhattan.
What cities and towns are in Riley County?
Riley County has 5 incorporated places. The most populous are Manhattan city, Ogden city, Riley city, Leonardville city, and Randolph city; 14,714 residents live outside any incorporated place.
Is Riley County part of a metropolitan area?
Yes. It is a central county of the Manhattan, KS Metropolitan Statistical Area, which has 3 county equivalents and 136,122 residents.
How many ZIP codes are in Riley County?
14 ZIP Code Tabulation Areas have land in Riley County, and 8 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Riley County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 1.7 times as much land.
How many acres of land are in Riley County?
The land measurement converts to approximately 390,182 acres. Including water, total area is approximately 398,113 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.