Plymouth, Illinois Demographics & Population 2026

A note before these figures: with a population of 456, Plymouth's ACS estimates come from a small number of survey responses and carry wide margins of error. Individual percentages below — particularly rates that round to 0% or 100% — are approximations, not precise measurements. See data.census.gov for the published margins of error.

Population Overview

Plymouth is a small community located in Illinois, within McDonough County. The total population is 456. It ranks as the 965th most populous out of 1,445 Census-designated places in Illinois.

Age Demographics

The median age in Plymouth is 51.3 years. This is 32% higher than the state median of 39.0 years. 13.8% of residents are 75 or older, suggesting a significant retirement-age population with implications for healthcare services and senior housing.

Economy, Income & Housing

The median household income in Plymouth is $41,071. This is 51% lower than the state median of $83,390. It is also 49% lower than the national median of $80,734. The poverty rate stands at 24.6%. This is 108% higher than the state poverty rate of 11.8%. With more than one in five residents living below the poverty line, economic hardship is a significant challenge for the community. The unemployment rate is 14.1%. This is 142% higher than the state rate of 5.8%. The median home value is $56,900. Housing costs are 78% lower than the state median of $263,300. With a home-value-to-income ratio of just 1.4x, Plymouth is one of the most affordable housing markets in the area. 84.4% of occupied housing units are owner-occupied. This homeownership rate is 26% higher than the state average of 67.1%.

Race & Ethnicity

Plymouth has a predominantly White (non-Hispanic) population, comprising 89.0% of all residents. Hispanic or Latino residents account for 4.4%. The White (non-Hispanic) population is significantly higher than the state average (89.0% vs 58.1%). The Black or African American population (2.2%) is well below the state average of 13.3%. The Hispanic or Latino population (4.4%) is well below the state average of 18.8%.

Education

8.0% of residents aged 25 and older hold a bachelor's degree or higher. This is 79% lower than the state rate of 37.9%. Nationally, 35.7% of adults hold at least a bachelor's degree. The high school graduation rate (or equivalent) is 81.1%.

Data Sources & Methodology

All demographic data for Plymouth, Illinois is sourced from the U.S. Census Bureau's American Community Survey (ACS) 2020–2024 5-Year Estimates. The ACS collects data from approximately 3.5 million households annually and pools five years of responses so that even small communities can be measured, though the margin of error widens as the population falls. Comparisons are made against Illinois state averages and national averages calculated from the same dataset. Rankings reflect the city's position among all 1,445 Census-designated places in Illinois. Read more about how these figures are produced on our methodology page, or visit data.census.gov for official data.