According to the United States Census Bureau, the city has a total area of 18.7 square miles (48.3 km²), of which, 18.6 square miles (48.3 km²) of it is land and 0.04 square miles (0.1 km²) of it (0.11%) is water.
There were 7,430 households out of which 32.5% had children under the age of 18 living with them, 54.8% were married couples living together, 12.9% had a female householder with no husband present, and 27.9% were non-families. 24.2% of all households were made up of individuals and 10.5% had someone living alone who was 65 years of age or older. The average household size was 2.54 and the average family size was 3.00.
In the city the population was spread out with 26.1% under the age of 18, 7.9% from 18 to 24, 27.5% from 25 to 44, 23.7% from 45 to 64, and 14.8% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 91.2 males. For every 100 females age 18 and over, there were 86.9 males.
The median income for a household in the city was $32,245, and the median income for a family was $37,558. Males had a median income of $30,524 versus $21,609 for females. The per capita income for the city was $17,266. About 11.5% of families and 12.9% of the population were below the poverty line, including 15.2% of those under age 18 and 17.4% of those age 65 or over.
Lorrie and Larry Collins, The Collins Kids, resided near Sapulpa in the early 1950s.