St. Petersburg is a borough in Clarion County, Pennsylvania, United States. The population was 338 at the 2020 census. St. Petersburg is located in western Clarion County at 41°09′39″N 79°39′14″W / 41.160944°N 79.653937°W. Pennsylvania Route 58 passes through the borough, leading 2 miles southwest to Foxburg on the Allegheny Riv…St. Petersburg is a borough in Clarion County, Pennsylvania, United States. The population was 338 at the 2020 census. St. Petersburg is located in western Clarion County at 41°09′39″N 79°39′14″W / 41.160944°N 79.653937°W. Pennsylvania Route 58 passes through the borough, leading 2 miles southwest to Foxburg on the Allegheny River and east 7 miles to Callensburg on the Clarion River. Pennsylvania Route 478 leads northwest 2 miles to Interstate 80 east of Emlenton.