Frost line depth in Niobrara County, WY
How deep the ground freezes in Niobrara County, WY
39 in. Dig to 39 in, just below the frost. Nearest NOAA station: Lance Creek 11nne, 10.8 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.