Today Petersburg is an independent city that does not belong to any county, but interacts directly with state government. Since 1871, all Virginia municipalities incorporated as "cities" are by law independent cities. There are 39 independent cities in Virginia, the most of any state. An independent city may serve as the county seat of an adjacent county, even though it is not a part of that county.
Petersburg grew from the former Fort Henry, established on the south bank of the Appomattox River in 1645. Fort Henry, built at the falls of the river, served as a frontier fort. The settlement that grew up around the fort was first named Peter's Point and then Petersburg in 1733 after Colonel William Byrd II led an expedition to survey the Virginia - North Carolina line. Byrd is credited with establishing both Richmond and Petersburg.
The city was formally organized in 1748, and, in 1784, the towns of Petersburg, Blandford, Pocahontas, and Ravenscroft were incorporated as the single town of Petersburg. Petersburg proper was in Dinwiddie, Pocahontas in Chesterfield, and Blandford and Ravenscroft in Prince George. Petersburg was established as an independent city in 1902.
Source: Phillip Slaughter, A History of Bristol Parish, Virginia, J. W. Randolph & English, Richmond (1846), http://www.archive.org/details/historyofbristol00inslau.
Independent City of Colonial Heights
Prince George County