According to the U.S. Census Bureau, the county has a total area of, of which is land and is water. King William County is bounded by the Mattaponi River to the north and the Pamunkey River to the south. The two rivers combine to form the York River, at West Point, the county's largest town.
As of the 2010 United States Census, there were 15,935 people living in the county. 77.2% were White, 17.7% Black or African American, 1.4% Native American, 0.7% Asian, 0.6% of some other race and 2.3% of two or more races. 2.0% were Hispanic or Latino. 18.6% were of English, 16.5% American, 8.7% German and 7.6% Irish ancestry. As of the census of 2000, there were 13,146 people, 4,846 households, and 3,784 families living in the county. The population density was 48 people per square mile. There were 5,189 housing units at an average density of 19 per square mile. The racial makeup of the county was 73.81% White, 22.81% Black or African American, 1.54% Native American, 0.37% Asian, 0.33% from other races, and 1.15% from two or more races. 0.91% of the population were Hispanic or Latino of any race. There were 4,846 households out of which 36.40% had children under the age of 18 living with them, 63.90% were married couples living together, 10.20% had a female householder with no husband present, and 21.90% were non-families. 18.30% of all households were made up of individuals and 7.60% had someone living alone who was 65 years of age or older. The average household size was 2.69 and the average family size was 3.06. In the county, the population was spread out with 26.10% under the age of 18, 5.90% from 18 to 24, 31.50% from 25 to 44, 24.80% from 45 to 64, and 11.70% who were 65 years of age or older. The median age was 37 years. For every 100 females, there were 96.90 males. For every 100 females age 18 and over, there were 93.90 males. The median income for a household in the county was $49,876, and the median income for a family was $54,037. Males had a median income of $34,616 versus $25,578 for females. The per capita income for the county was $21,928. About 4.40% of families and 5.50% of the population were below the poverty line, including 6.00% of those under age 18 and 9.00% of those age 65 or over. Two Indian reservations exist in the county. They are the only ones in the Commonwealth of Virginia
Government
Board of Supervisors
First District: William L. Hodges
Second District: Travis J. Moskalski
Third District: Stephen K. Greenwood
Fourth District: David E. Hansen
Fifth District: Robert W. Ehrhart
Constitutional officers
Clerk of the Circuit Court: Patricia M. Norman
Commissioner of the Revenue: Sally W. Pearson
Commonwealth's Attorney: Matthew R. Kite
Sheriff: J.S. "Jeff" Walton
Treasurer: Harry L. Whitt
King William is represented by Republican Thomas K. "Tommy" Norment, Jr. in the Virginia Senate, Republicans Christopher K. "Chris" Peace and M. Keith Hodges in the Virginia House of Delegates, and Republican Robert J. "Rob" Wittman.