Petersburg is a borough in Huntingdon County, Pennsylvania, United States. It was a stop on the former Pennsylvania Railroad Main Line between Tyrone and Huntingdon and the junction point for the Petersburg Branch. The population was 480 at the 2010 census.Petersburg is located in northern Huntingdon County at 40°34′21″N 78°2′53″W / 40.57250°N 78.04806°W / 40.57250; -78.04806. It sits on the east side of Shaver Creek where it joins the Juniata River, just east of that river's source at the confluence of the Little Juniata River and the Frankstown Branch.Pennsylvania Route 305 passes through Petersburg, leading northeast 19 miles to Greenwood Furnace State Park and west 3 miles to Alexandria. Huntingdon, the county seat, is 9 miles to the south via local roads.According to the United States Census Bureau, the borough has a total area of 0.33 square miles, all of it land.As of the census of 2000, there were 455 people, 177 households, and 132 families residing in the borough.