County Maps US

Montgomery County, Illinois

A county in Illinois, ranked 48 of 102 by population.

CountyFIPS 17135

Within Illinois
Montgomery County, highlighted, with the areas around it. Boundaries generalised from the 2025 Census cartographic boundary file; neighbour fills carry no data. The dot marks Hillsboro, the county seat, located via the 2025 Census Gazetteer.

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Population
28,076
-168 (-0.6%) since 2020
Land area
703.8
square miles. A further 0.8% of the total area is water
Population density
39.9
people per square mile, computed rather than published
County seat
Hillsboro
Seat of county government.
Established
1821
204 years ago
Largest city
Litchfield city
Population 6,598.

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; Wikidata (CC0), Wikidata. Retrieved 30 August 2026.

Satellite view

Aerial imagery of Montgomery County with its boundary drawn on top. A map shows you the shape; this shows you what is inside it, and which side of the line a place falls on.

Aerial view of Montgomery County, Illinois from the USGS National Map, with its boundary outlined
Imagery: USGS National Map, USGS Imagery Only, public domain, requested from USGS by your browser when you reach this point on the page, at 679 by 800 pixels. The boundary is the 2025 Census cartographic boundary file, reprojected to Web Mercator to match the imagery. You can also open the USGS National Map viewer.

Where Montgomery County ranks

Position among the 102 counties of Illinois, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn IllinoisNationally
Population28,07648th of 1021,508th of 3,144
Land area703.8 sq mi25th of 1021,318th of 3,144
Population density39.9 per sq mi58th of 1021,677th of 3,144
Median household income$63,62066th of 1021,741st of 3,143

Full data for Montgomery County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population28,076Vintage 2025 Population Estimates
Population in 202028,244Vintage 2025 Population Estimates
2020 estimates base?28,327Vintage 2025 Population Estimates
Land area703.8 sq mi2025 Gazetteer Files
Water area6.0 sq mi2025 Gazetteer Files
Total area709.7 sq mi2025 Gazetteer Files
Population density?39.9 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$63,620American Community Survey 2020-2024 5-Year Estimates
Median home value$112,300American Community Survey 2020-2024 5-Year Estimates
Median age42.8American Community Survey 2020-2024 5-Year Estimates
Households11,319American Community Survey 2020-2024 5-Year Estimates
Housing units12,495American Community Survey 2020-2024 5-Year Estimates

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Population density is computed here, not published: it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, which are two different Census products. Retrieved 30 August 2026.

How the population changed

The Census Bureau publishes the components behind an estimate, not just the total. For the year to July 2025:

Births minus deaths
-92
247 births, 339 deaths
Net migration
+333
More people moved in than moved out.

Source: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026. Retrieved 30 August 2026.

The 7 areas bordering Montgomery County

Ordered by the length of the border actually shared, which the Census Bureau publishes in its county adjacency file and which no other county reference presents.

Bordering areaStateShared borderPopulation
Macoupin CountyIllinois36 mi43,748
Christian CountyIllinois33 mi33,443
Bond CountyIllinois23 mi16,959
Fayette CountyIllinois19 mi20,790
Shelby CountyIllinois9.0 mi20,576
Sangamon CountyIllinois9.0 mi194,170
Madison CountyIllinois3.2 mi263,110

Source: US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. Retrieved 30 August 2026.

All 102 counties of Illinois

Open the interactive Illinois county map, or jump straight to any of them.

Data on this page last rebuilt 30 August 2026. How these figures are produced.