Frost line depth in Barnstable County, MA
How deep the ground freezes in Barnstable County, MA
9 in. Dig to 12 in, the 12 in code minimum. Nearest NOAA station: W Harwich, 3.9 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.