Frost line depth in Olmsted County, MN
How deep the ground freezes in Olmsted County, MN
50 in. Dig to 50 in, just below the frost. Nearest NOAA station: Rochester Intl Ap, 7.7 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.