Penhook is a census-designated place in Franklin County, Virginia, United States. The population was 801 at the 2010 census, up from 726 in 2000. It is part of the Roanoke metropolitan area. Penhook is located in eastern Franklin County at 37°0′16″N 79°37′43″W / 37.00444°N 79.62861°W. It is bordered to the east by the Pittsylvania County line and by the Cool …Penhook is a census-designated place in Franklin County, Virginia, United States. The population was 801 at the 2010 census, up from 726 in 2000. It is part of the Roanoke metropolitan area. Penhook is located in eastern Franklin County at 37°0′16″N 79°37′43″W / 37.00444°N 79.62861°W. It is bordered to the east by the Pittsylvania County line and by the Cool Branch arm of Smith Mountain Lake. The northern edge of the CDP is the center of the Blackwater River part of the lake, while the northwestern edge follows the Bull Run arm of the lake and then Bull Run itself upstream to Virginia State Route 40, which runs east–west through the center of the CDP. The southern half of the CDP extends nearly to the Pigg River, an east-flowing tributary of the Roanoke River. Route 40 leads west 17 miles to Rocky Mount, the Franklin County seat, and east 16 miles to Gretna at U.S. Route 29.