The native Pennacook tribe called the area Contoocook, meaning "place of the river near pines." On June 6, 1733, Governor Jonathan Belcher granted it to John Coffin and 90 others, most from Newbury, Massachusetts. Settled in 1734, it soon had a meetinghouse, sawmill, gristmill and ferry across the Merrimack River. A garrison offered protection, but guerrilla attacks during the French and Indian Wars left some dead or carried into captivity.
On April 22, 1760, Contoocook Plantation was incorporated as a town by Governor Benning Wentworth, who named it for Edward Boscawen, the British admiral who distinguished himself at the 1758 Siege of Louisbourg. With a generally level surface, the town provided good farmland, and became noted for its apple, pear and cherry orchards. Bounded by the Merrimack and Contoocook rivers, it had abundant sources of water power for mills.
Industries soon included a cotton mill, a woolen factory, nine sawmills, a gristmill, a saw manufacturer and machine shop, and a chair and match factory. A mill town village developed at Fisherville (now Penacook), which straddled the river border with Concord. In 1846, the Northern Railroad was built through Boscawen, opening the following winter.
Sometime around 1846, the town's postmaster became one of about a dozen in the country to issue provisional postage stamps before the official issue came out in 1847. The stamps were an adaptation of a postmark, simply reading PAID / 5 / CENTS, typeset in blue on a yellowish paper. These are extremely rare; in 2003, the estimated price at auction was US$225,000.