As of the census of 2000, there were 130,449 people, 48,941 households, and 37,048 families residing in the county. The population density was 246 people per square mile (95/km²). There were 51,657 housing units at an average density of 98 per square mile (38/km²). The racial makeup of the county was 91.49% White, 5.78% Black or African American, 0.29% Native American, 0.66% Asian, 0.03% Pacific Islander, 0.80% from other races, and 0.96% from two or more races. 1.76% of the population were Hispanic or Latino of any race.
By 2005 89.1% of Sumner County's population was non-Hispanic whites while 6.5% was African-American and 2.5% was Latino.
In 2000 there were 48,941 households out of which 36.30% had children under the age of 18 living with them, 61.10% were married couples living together, 10.80% had a female householder with no husband present, and 24.30% were non-families. 20.30% of all households were made up of individuals and 7.20% had someone living alone who was 65 years of age or older. The average household size was 2.64 and the average family size was 3.04.
In the county, the population was spread out with 26.30% under the age of 18, 8.00% from 18 to 24, 30.70% from 25 to 44, 24.30% from 45 to 64, and 10.70% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 95.90 males. For every 100 females age 18 and over, there were 92.30 males.
The median income for a household in the county was $46,030, and the median income for a family was $52,125. Males had a median income of $36,875 versus $25,720 for females. The per capita income for the county was $21,164. About 6.20% of families and 8.10% of the population were below the poverty line, including 10.50% of those under age 18 and 10.00% of those age 65 or over.