According to the U.S. Census Bureau, the county has a total area of, of which is land and is water. Most of eastern Polk County, centered on Rockmart, is located in the Etowah River sub-basin of the ACT River Basin, while most of western Polk County, centered on Cedartown, is located in the Upper Coosa River sub-basin of the same ACT River Basin. Small slivers of the southern edges of the county are located in the Upper Tallapoosa River sub-basin of the same larger ACT River Basin.
As of the census of 2000, there were 38,127 people, 14,012 households, and 10,340 families living in the county. The population density was 122 people per square mile. There were 15,059 housing units at an average density of 48 per square mile. The racial makeup of the county was 80.52% White, 13.34% Black or African American, 0.22% Native American, 0.31% Asian, 0.04% Pacific Islander, 4.62% from other races, and 0.95% from two or more races. 7.66% of the population were Hispanic or Latino of any race. There were 14,012 households out of which 32.90% had children under the age of 18 living with them, 55.90% were married couplesliving together, 13.10% had a female householder with no husband present, and 26.20% were non-families. 22.70% of all households were made up of individuals and 10.50% had someone living alone who was 65 years of age or older. The average household size was 2.66 and the average family size was 3.09. In the county, the population was spread out with 26.10% under the age of 18, 9.70% from 18 to 24, 28.80% from 25 to 44, 22.30% from 45 to 64, and 13.20% who were 65 years of age or older. The median age was 35 years. For every 100 females, there were 99.20 males. For every 100 women age 18 and over, there were 95.70 men. The median income for a household in the county was $32,328, and the median income for a family was $37,847. Males had a median income of $29,985 versus $21,452 for females. The per capita income for the county was $15,617. About 11.20% of families and 15.50% of the population were below the poverty line, including 18.70% of those under age 18 and 12.60% of those age 65 or over.
2010 census
As of the 2010 United States Census, there were 41,475 people, 15,092 households, and 10,908 families living in the county. The population density was. There were 16,908 housing units at an average density of. The racial makeup of the county was 77.1% white, 12.5% black or African American, 0.7% Asian, 0.3% American Indian, 0.1% Pacific islander, 7.5% from other races, and 1.8% from two or more races. Those of Hispanic or Latino origin made up 11.8% of the population. In terms of ancestry, 17.2% were English, 15.2% were American, 13.0% were Irish, and 5.3% were German. Of the 15,092 households, 38.2% had children under the age of 18 living with them, 51.5% were married couples living together, 14.8% had a female householder with no husband present, 27.7% were non-families, and 23.6% of all households were made up of individuals. The average household size was 2.72 and the average family size was 3.20. The median age was 36.2 years. The median income for a household in the county was $38,646 and the median income for a family was $43,172. Males had a median income of $37,070 versus $27,758 for females. The per capita income for the county was $18,214. About 15.6% of families and 19.3% of the population were below the poverty line, including 25.4% of those under age 18 and 10.5% of those age 65 or over.
