Frost line depth in Mercer County, PA
How deep the ground freezes in Mercer County, PA
31 in. Dig to 31 in, just below the frost. Nearest NOAA station: Mercer, 5.3 mi.
Your building department sets the legal frost line depth (IRC Table R301.2(1)); footings must go below it (R403.1.4.1). Call them before you dig.