Madison County area

Population and density of Madison County

The Census Bureau estimates that 55,172 people lived in Madison County on July 1, 2025. That ranks #959 of 3,222 county equivalents nationally and #7 of 44 in Idaho. Since the April 1, 2020 estimates base of 52,913, the population has grown by 2,259 (+4.3%), compared with +10.4% for Idaho as a whole.

With 469.3 square miles of land, that is 118 people per square mile (45 per km²), placing Madison County #887 nationally for density and #4 in Idaho. The median county equivalent has 47 people per square mile; the Idaho median is 10. Put another way, there are about 5.4 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 Madison County

2 incorporated places lie at least partly in Madison County. Together they are home to 42,810 people (77.6%); the other 12,362 (22.4%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Rexburg city, with 40,334 residents in the county. Among places with at least 1,000 residents in 2020, Sugar City city grew fastest since then (+43.8%).

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

Metropolitan area

Madison County is a central county of the Rexburg, ID Micropolitan Statistical Area. Its 2 county equivalents have 69,380 residents on 2,333.2 square miles of land; Madison County accounts for 20.1% of the land and 79.5% of the residents. By combined land it ranks #65 of 542 micropolitan areas, and #114 by population. It belongs to the Idaho Falls-Rexburg-Blackfoot, ID Combined Statistical Area.

ZIP codes

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

8343483436834408344383445834488345183460

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 Madison County

Madison County shares a land border with 4 county equivalents. It has more land than 1 of them. The largest neighbor is Bonneville County (1,866 mi²) and the smallest is Teton County (449.1 mi²). Together with its neighbors, Madison County forms a block of 5,742 mi² of land, of which it holds 8.2%.

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

Madison County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2.2 times as much. Idaho’s county land could hold about 176 areas the size of Madison County.

Another way to picture it: the same land area would fill a square about 21.7 miles (34.9 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 Madison County?

Madison County has more land than 1,027 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 Madison County at #2,269 nationally by total area, 74 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 0.9%, compared with a national county-equivalent median of 1.2% — 0.3 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 Madison 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.