Petersburg Census Area was a census area in the U.S. state of Alaska. It was part of the Unorganized Borough and therefore has no borough seat. Its largest community was Petersburg. The population was 3,815 at the 2010 census. It was previously known as the Wrangell-Petersburg Census Area until June 1, 2008, when Wrangell, formerly a part of the census area, was incorporated as a city-and-borough.