According to the U.S. Census Bureau, the county has a total area of, of which is land and is water. It is located in the Piedmont region of the state. The vast majority of Monroe County is located in the Upper Ocmulgee River sub-basin of the Altamaha River basin, with just a tiny southwestern corner of the county, west of a line between Yatesville and Culloden, located in the Upper Flint River sub-basin of the ACF River Basin.
As of the census of 2000, there were 21,757 people, 7,719 households, and 6,005 families living in the county. The population density was 21/km². There were 8,425 housing units at an average density of 8/km². The racial makeup of the county was 70.36% White, 27.93% Black, 0.35% Native American, 0.34% Asian, 0.03% Pacific Islander, 0.25% from other races, and 0.74% from two or more races. 1.29% of the population were Hispanic or Latino of any race. There were 7,719 households out of which 35.80% had children under the age of 18 living with them, 59.60% were married couplesliving together, 13.80% had a female householder with no husband present, and 22.20% were non-families. 18.90% of all households were made up of individuals and 7.40% had someone living alone who was 65 years of age or older. The average household size was 2.74 and the average family size was 3.12. In the county, the population was spread out with 26.30% under the age of 18, 8.30% from 18 to 24, 30.40% from 25 to 44, 24.70% from 45 to 64, and 10.30% who were 65 years of age or older. The median age was 36 years. For every 100 females, there were 99.40 males. For every 100 females age 18 and over, there were 97.20 males. The median income for a household in the county was $44,195, and the median income for a family was $51,093. Males had a median income of $34,433 versus $22,146 for females. The per capita income for the county was $19,580. About 7.30% of families and 9.80% of the population were below the poverty line, including 12.00% of those under age 18 and 13.30% of those age 65 or over.
2010 census
As of the 2010 United States Census, there were 26,424 people, 9,662 households, and 7,157 families living in the county. The population density was. There were 10,710 housing units at an average density of. The racial makeup of the county was 73.3% white, 23.7% black or African American, 0.8% Asian, 0.3% American Indian, 0.9% from other races, and 1.0% from two or more races. Those of Hispanic or Latino origin made up 2.0% of the population. In terms of ancestry, 14.7% were American, 13.1% were English, 9.9% were German, and 9.5% were Irish. Of the 9,662 households, 33.6% had children under the age of 18 living with them, 56.2% were married couples living together, 13.1% had a female householder with no husband present, 25.9% were non-families, and 21.9% of all households were made up of individuals. The average household size was 2.61 and the average family size was 3.03. The median age was 41.3 years. The median income for a household in the county was $48,297 and the median income for a family was $61,110. Males had a median income of $41,409 versus $32,810 for females. The per capita income for the county was $23,656. About 9.8% of families and 12.3% of the population were below the poverty line, including 15.3% of those under age 18 and 12.9% of those age 65 or over.
