City · Illinois
Monmouth, Illinois
Monmouth, city, in Warren County, Illinois. Monmouth had 8,599 residents on July 1, 2025 by the Census Bureau's estimate, down 3.7% since 2020; the 2020 Census counted 8,902 and the ACS 2020-2024 5-year estimates put it at 8,581 (±285). GEOID 1750010.
Residents, July 2025 estimate
8,599
Census Bureau estimate (no margin published)
2020 Census count: 8,902 · ACS 2020-2024: 8,581 ±285
Median household income
$61,138
±$7,127 (90% margin)
Illinois: $83,390
Median home value
$86,800
±$6,933 (90% margin)
Illinois: $263,300
Median gross rent
$733
±$68 (90% margin)
Illinois: $1,274
Where is Monmouth and what county is it in?
Monmouth is a city in Warren County, Illinois. It covers 4.2 square miles of land, 2,098 residents per square mile in 2020.
Monmouth lies entirely within Monmouth Township, a township with its own local government (2020 census blocks).
Source: 2024 Gazetteer and 2020 place-by-county files, U.S. Census Bureau · Census reference files
How many people live in Monmouth, and is it growing?
The Census Bureau estimates that 8,599 people lived in Monmouth on July 1, 2025, down 3.7% since 2020, a steeper fall than Illinois's (−0.8%). The 2020 Census counted 8,902 residents. The 2020-2024 American Community Survey, a five-year sample, puts the population at 8,581 (±285).
| Measure | Monmouth | Warren County | Change since 2015-2019 |
|---|---|---|---|
| Total population | 8,581 ±285 | 16,447 | no clear change |
| Households | 3,323 ±258 | 6,787 | no clear change |
| Average household size | 2.29 ±0.16 | 2.27 | no clear change |
| Housing units | 3,750 ±212 | 7,587 | no clear change |
Monmouth's population since 2000
From 9,841 in 2000 to 8,599 in 2025: down 12.6%. The 2000, 2010 and 2020 figures are census counts, each for Monmouth as it was drawn that year: a place that annexed land, or a community that has since incorporated, covered a different area then. The 2005 figure is the Census Bureau's intercensal estimate, revised to fit the 2000 and 2010 counts and drawn on 2010 boundaries; 2015 and 2025 are July 1 estimates made from the census before them.
Source: The 2000, 2010 and 2020 Census counts and the Census Bureau's population estimates (intercensal 2000-2010, Vintage 2020, Vintage 2025) · Census population estimates
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026); Census PEP Vintage 2025 (SUB-EST2025, CO-EST2025); 2020 Census P.L. 94-171 · Check it at data.census.gov
Who lives in Monmouth?
The median resident of Monmouth is 34.1 years old; 23.8% are under 18 and 15.9% are 65 or older. The largest group is non-Hispanic white residents at 70.4%, then Hispanic or Latino residents (of any race) at 18.1%. 10.5% of residents were born outside the United States.
| Measure | Monmouth | Warren County | Change since 2015-2019 |
|---|---|---|---|
| Median age | 34.1 ±1.5 | 38.5 | no clear change |
| Under 18 years | 23.8% ±1.9 pts | 22.5% | – |
| 65 years and over | 15.9% ±2.2 pts | 20.0% | – |
| Male | 48.3% ±2.2 pts | 50.3% | – |
| Hispanic or Latino (any race) | 18.1% ±1.4 pts | 11.1% | +4.4 pts |
| White alone, not Hispanic | 70.4% ±2.2 pts | 81.1% | −3.9 pts |
| Black or African American alone, not Hispanic | 4.5% ±1.6 pts | 2.7% | no clear change |
| Asian alone, not Hispanic | 4.1% ±1.0 pts | 2.4% | no clear change |
| American Indian and Alaska Native alone, not Hispanic | 0.2% ±0.2 pts | 0.1% | – |
| Native Hawaiian and Other Pacific Islander alone, not Hispanic | 0.3% ±0.4 pts | 0.1% | – |
| Two or more races, not Hispanic | 2.0% ±1.3 pts | 2.1% | – |
| Some other race alone, not Hispanic | 0.4% ±0.8 pts | 0.3% | – |
| Born outside the United States | 10.5% ±1.9 pts | 6.5% | no clear change |
| Speak a language other than English at home (age 5+) | 18.4% ±2.6 pts | 12.0% | – |
| Civilian veterans (age 18+) | 5.1% ±1.7 pts | 7.3% | – |
| With a disability | 14.1% ±2.5 pts | 13.8% | – |
| No health insurance coverage | 5.5% ±2.5 pts | 5.0% | no clear change |
| High school graduate or higher (age 25+) | 84.0% ±3.3 pts | 87.1% | – |
| Bachelor's degree or higher (age 25+) | 18.3% ±3.5 pts | 22.0% | no clear change |
| Graduate or professional degree (age 25+) | 6.9% ±2.2 pts | 7.9% | – |
| Lived in the same house a year earlier | 83.4% ±4.0 pts | 87.6% | – |
| Moved from another state in the past year | 2.0% ±1.2 pts | 1.4% | – |
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026) (Data Profiles DP02, DP05) · Check it at data.census.gov
What do households in Monmouth earn?
Half of Monmouth's 3,323 households earn less than $61,138 a year (±$7,127), against $67,385 in Warren County and $83,390 in Illinois. In 2015-2019 it was $54,196 in 2024 dollars; the margins of error cannot tell the two periods apart. 17.7% of residents live below the poverty line.
| Measure | Monmouth | Warren County | Change since 2015-2019 |
|---|---|---|---|
| Median household income | $61,138 ±$7,127 | $67,385 | no clear change |
| Mean household income | $76,717 ±$8,700 | $86,803 | – |
| Per capita income | $29,501 ±$3,382 | $35,164 | no clear change |
| People below the poverty line | 17.7% ±4.2 pts | 14.6% | no clear change |
| Children under 18 below the poverty line | 31.0% ±10.6 pts | 24.8% | no clear change |
| Households receiving SNAP | 23.7% ±4.9 pts | 16.0% | – |
| Households with a computer | 93.3% ±3.1 pts | 93.0% | – |
| Households with a broadband subscription | 85.6% ±4.4 pts | 84.7% | – |
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026) (Data Profile DP03) · Check it at data.census.gov
What does housing cost in Monmouth?
Owners occupy 66.3% of Monmouth's occupied homes and renters 33.7%. The median owner-occupied home is valued at $86,800 by its owner (±$6,933). The median renter pays $733 a month including utilities, and 26.4% of renters pay 35% or more of their income on rent.
| Measure | Monmouth | Warren County | Change since 2015-2019 |
|---|---|---|---|
| Median home value (owner-occupied) | $86,800 ±$6,933 | $105,000 | no clear change |
| Median gross rent | $733 ±$68 | $788 | no clear change |
| Renters paying 35% or more of income on rent | 26.4% ±11.0 pts | 26.5% | no clear change |
| Median monthly owner costs, with a mortgage | $974 ±$115 | $1,059 | – |
| Owner-occupied homes | 66.3% ±5.2 pts | 75.2% | no clear change |
| Renter-occupied homes | 33.7% ±5.2 pts | 24.8% | – |
| Housing units | 3,750 ±212 | 7,587 | no clear change |
| Homeowner vacancy rate | 1.0% ±1.1 pts | 0.6% | – |
| Rental vacancy rate | 3.2% ±5.0 pts | 3.3% | – |
| Single-family detached homes | 78.6% ±4.7 pts | 87.3% | – |
| Mobile homes | 3.5% ±2.3 pts | 2.6% | – |
| Built 2020 or later | 0.9% ±1.3 pts | 0.5% | – |
| Built 2010 to 2019 | 0.3% ±0.4 pts | 1.6% | – |
| Built 1939 or earlier | 37.0% ±5.5 pts | 33.9% | – |
| Households with no vehicle | 10.9% ±3.1 pts | 6.9% | – |
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026) (Data Profile DP04) · Check it at data.census.gov
How many new homes is Monmouth building?
Builders took permits for 0 new housing units in Monmouth in 2025 (0 in single-family houses), 0.0 per 1,000 residents against 1.5 across Illinois.
Counts of units in permits a local office issued; not every permitted unit is built. A year marked with months was reported for part of the year.
Source: Building Permits Survey, annual place files 2019-2025, U.S. Census Bureau · Census Building Permits Survey
How do people in Monmouth work and get to work?
75.0% of Monmouth's workers drive alone and 7.5% work from home. The average trip to work takes 15.5 minutes. The unemployment rate in 2020-2024 averaged 3.6%.
| Measure | Monmouth | Warren County | Change since 2015-2019 |
|---|---|---|---|
| In the labor force (age 16+) | 63.9% ±3.5 pts | 61.0% | – |
| Unemployment rate | 3.6% ±2.2 pts | 3.6% | −8.0 pts |
| Drove alone to work | 75.0% ±4.8 pts | 80.5% | – |
| Carpooled | 7.8% ±2.6 pts | 5.6% | – |
| Public transportation | 1.3% ±1.3 pts | 0.7% | – |
| Walked | 6.5% ±2.7 pts | 4.6% | – |
| Worked from home | 7.5% ±2.3 pts | 7.4% | +5.1 pts |
| Mean travel time to work | 15.5 min ±2.4 | 18.8 min | no clear change |
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026) (Data Profile DP03) · Check it at data.census.gov
What census tracts are in Monmouth?
2 census tracts lie mostly in Monmouth, and 1 more reaches into it (2020 census blocks). Their median household incomes run from $61,225 (Tract 8704) to $63,345 (Tract 8705).
| Tract | Residents, 2020-2024 | Median household income |
|---|---|---|
| Tract 8704Warren County | 4,600 | $61,225 |
| Tract 8705Warren County | 4,620 | $63,345 |
| Tract 8703Warren County | 2,472 | $65,000 |
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026); 2020 block assignment files (tract share = share of the tract's census blocks in Monmouth) · Census block assignment files
How does Monmouth compare with other places in Illinois?
By the Census Bureau's July 2025 estimates, Monmouth is the 3,566th-most populous of the 19,476 U.S. incorporated places that have one and the 249th-most populous of 1,294 in Illinois.
Monmouth ranks 1,066th of 1,380 places in Illinois with 1,000 or more residents and a reliable estimate, by median household income.
| Measure | Rank | Of |
|---|---|---|
| Population, July 2025 estimate | 249th | 1,294 |
| Growth 2020-2025 (PEP) | 1,162nd | 1,347 |
| Residents per square mile | 259th | 1,383 |
| Median household income | 1,066th | 1,380 |
| Per capita income | 1,200th | 1,383 |
| Median home value | 1,278th | 1,379 |
| Median gross rent | 1,112th | 1,280 |
| Poverty rate | 187th | 1,119 |
| Bachelor's degree or higher | 982nd | 1,369 |
| Median age | 1,292nd | 1,383 |
| Owner-occupied share | 1,153rd | 1,382 |
| Work from home | 798th | 1,015 |
| Travel time to work | 1,342nd | 1,382 |
Monmouth's figures with every place in Illinois (CSV)
Every place in Illinois, sortable · Compare Monmouth with other places
Source: PlainCities ranks computed from the American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026) and PEP Vintage 2025 · How ranks are computed
How reliable are the figures for Monmouth?
8 of the 57 figures for Monmouth on this page carry a coefficient of variation over 40% and are marked with a ring: they come from a small sample, so read them as rough.
The American Community Survey samples about one household in eight over five years, so every figure is an estimate with a 90% margin of error (shown under each value). A ring marks an estimate whose coefficient of variation is over 40%. A change is called only when the gap between the two periods is larger than their combined 90% margin (the square root of the sum of the two squared margins), the Census Bureau's test. How to read a margin of error.
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026): margins of error as published · ACS technical documentation
How these figures are made: methodology and release checks · reading a margin of error · every state · corrections
Not on this page: crime, weather and schools for Monmouth are other agencies' records. Crime: the FBI's Crime Data Explorer · climate: NOAA's U.S. Climate Normals · schools: the National Center for Education Statistics' public schools in Monmouth.