Putnam County is part of the Charleston, WV metropolitan area, with a 2006 Census population estimate of 305,526 people.
According to the U.S. Census Bureau, the county has a total area of 350 square miles (908 km²), of which, 346 square miles (897 km²) of it is land and 4 square miles (11 km²) of it (1.19%) is water.
Since the county is roughly equidistant between Charleston and Huntington, the state's two largest cities, along Interstate 64, the area has undergone a period of rapid suburbanization. Areas that were once farms or wooded backcountry are now being developed into subdivisions. In fact, the area is now the second-fastest growing region of West Virginia, following the sections of the Eastern Panhandle that are near Washington, DC.
Controversial lottery winner Jack Whittaker lives in Putnam County; he won the multi-state Powerball jackpot on December 25, 2002.
As of the census of 2000, there were 51,589 people, 20,028 households, and 15,281 families residing in the county. The population density was 149 people per square mile (58/km²). There were 21,621 housing units at an average density of 62 per square mile (24/km²). The racial makeup of the county was 97.97% White, 0.56% Black or African American, 0.16% Native American, 0.58% Asian, 0.02% Pacific Islander, 0.13% from other races, and 0.59% from two or more races. 0.51% of the population were Hispanics or Latinos of any race.
There were 20,028 households out of which 35.40% had children under the age of 18 living with them, 64.20% were married couples living together, 8.90% had a female householder with no husband present, and 23.70% were non-families. 20.60% of all households were made up of individuals and 7.90% had someone living alone who was 65 years of age or older. The average household size was 2.56 and the average family size was 2.96.
The age distribution was 25.00% under the age of 18, 7.60% from 18 to 24, 30.40% from 25 to 44, 25.50% from 45 to 64, and 11.60% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 96.70 males. For every 100 females age 18 and over, there were 93.50 males.
The median income for a household in the county was $41,892, and the median income for a family was $48,674. Males had a median income of $40,782 versus $23,532 for females. The per capita income for the county was $20,471. About 7.10% of families and 9.30% of the population were below the poverty line, including 11.30% of those under age 18 and 7.60% of those age 65 or over.