Christiansburg is a town in Montgomery County, Virginia, United States. The population was 16,947 at the 2000 census and was estimated to have increased to 19,477 in 2008, an increase of 14.9%. It is the county seat of Montgomery County. Christiansburg, Blacksburg, and Radford are the three principal municipalities of the Blacksburg-Christiansburg-Radford Metropolitan Statistical Area which encompasses those municipalities and all of Montgomery County.