N.H. Rev. Stat. Ann. § 22:3

The county of Strafford is bounded thus: Beginning at the northerly corner of the town of Northwood; thence by the westerly lines of the towns of Strafford and New Durham to the northerly corner of New Durham; thence by the northerly lines of New Durham, Middleton and Milton to the state line; thence down said line to the county of Rockingham; thence by the northerly line of the county of Rockingham to the bound first mentioned.