Chesterfield County is a county located just south of Richmond in the Commonwealth of Virginia. The county borders are primarily defined by the James River to the north, and the Appomattox River to the South. Its county seat is Chesterfield Court House. Chesterfield County was formed in 1749 from parts of Henrico County. It was named for Philip Stanhope, 4th Earl of Chesterfield, a prominent English statesman who had been the Lord Lieutenant of Ireland. Chesterfield County is largely bordered by two rivers which define miles of its boundaries. The major adjoining cities each originated at the head of navigation of these river, called the fall line. There, the hillier and rockier Piedmont region falls to the sandy and mostly flat eastern coastal plain Tidewater region, a change which creates barriers for ships going upstream on the rivers. Chesterfield County includes areas of both regions. Richmond and Manchester were formed at the fall line of the James River. Most of the northern portion of Chesterfield County is part of what is called Richmond's "South Side". As the James River flows east to Richmond and then turns almost due south below the fall line for about 8 miles (13 km) before turning east, Henrico County encompasses much of Richmond's West End, North Side, and East End areas. Chesterfield County borders on the Appomattox River to the south. Much of the southern and eastern portions of the county are considered part of the Tri-Cities area, which includes Petersburg, located at the fall line.