Frost line depth in Lyon County, MN
How deep the ground freezes in Lyon County, MN
52 in. Dig to 52 in, just below the frost. Nearest NOAA station: Marshall, 5.2 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.