Adjacent counties

• Union County (north)
• Franklin County (east)
• Pickaway County (southeast)
• Fayette County (south)
• Greene County (southwest)
• Clark County (west)
• Champaign County (northwest)

2000 census

As of the census^[19] of 2000, there were 40,213 people, 13,672 households, and 10,035 families living in the county. The population density was 86 inhabitants per square mile (33/km²). There were 14,399 housing units at an average density of 31 units per square mile (12/km²). The racial makeup of the county was 91.75% White, 6.24% Black or African American, 0.20% Native American, 0.44% Asian, 0.01% Pacific Islander, 0.35% from other races, and 1.01% from two or more races. 0.73% of the population were Hispanic or Latino of any race.

There were 13,672 households, out of which 35.20% had children under the age of 18 living with them, 59.20% were married couples living together, 9.90% had a female householder with no husband present, and 26.60% were non-families. 22.30% of all households were made up of individuals, and 9.50% had someone living alone who was 65 years of age or older. The average household size was 2.62 and the average family size was 3.06.

In the county, the population was spread out, with 24.70% under the age of 18, 9.10% from 18 to 24, 32.80% from 25 to 44, 22.60% from 45 to 64, and 10.90% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 117.00 males. For every 100 females age 18 and over, there were 121.30 males.

The median income for a household in the county was $44,212, and the median income for a family was $50,520. Males had a median income of $35,251 versus $26,119 for females. The per capita income for the county was $18,721. About 6.20% of families and 7.80% of the population were below the poverty line, including 10.50% of those under age 18 and 8.70% of those age 65 or over.

2010 census

As of the 2010 United States Census, there were 43,435 people, 14,734 households, and 10,580 families living in the county.^[20] The population density was 93.2 inhabitants per square mile (36.0/km²). There were 15,939 housing units at an average density of 34.2 units per square mile (13.2 units/km²).^[21] The racial makeup of the county was 90.6% white, 6.6% black or African American, 0.5% Asian, 0.2% American Indian, 0.5% from other races, and 1.5% from two or more races. Those of Hispanic or Latino origin made up 1.4% of the population.^[20] In terms of ancestry, 32.0% were German, 16.5% were Irish, 14.5% were American, and 9.6% were English.^[22]

Of the 14,734 households, 34.1% had children under the age of 18 living with them, 55.4% were married couples living together, 11.3% had a female householder with no husband present, 28.2% were non-families, and 23.5% of all households were made up of individuals. The average household size was 2.59 and the average family size was 3.04. The median age was 39.1 years.^[20]

The median income for a household in the county was $50,533 and the median income for a family was $63,397. Males had a median income of $46,550 versus $33,193 for females. The per capita income for the county was $23,980. About 8.9% of families and 11.7% of the population were below the poverty line, including 16.1% of those under age 18 and 6.1% of those age 65 or over.^[23]

City

• London (county seat)

Villages

• Midway
• Mount Sterling
• Plain City
• South Solon
• West Jefferson

Townships

Census-designated places

• Choctaw Lake
• Lafayette
• Plumwood

Unincorporated communities