Frost line depth in Polk County, NE
How deep the ground freezes in Polk County, NE
34 in. Dig to 34 in, just below the frost. Nearest NOAA station: Osceola, 1 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.