Frost line depth in Bergen County, NJ
How deep the ground freezes in Bergen County, NJ
17 in. Dig to 17 in, just below the frost. Nearest NOAA station: Teterboro Ap, 7.6 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.