Some 500 families inhabited the new town. Shipbuilding was a growing industry. In 1766, 72 vessels were built and in 1772, 90 vessels were launched. Most were purchased by England. By the third quarter of the 18th century, “Newbury Port” had become the center of New England shipbuilding. West Indian trade was brisk on the eve of the Revolution. Between 1756 and 1765, 427 Newbury-built vessels entered Customs at Salem or Boston.

In September 1775, early in the American Revolutionary War, Colonel Benedict Arnold led a force of 1,100 Continental Army troops on an expedition from Newburyport to Quebec City. The expedition was part of a two-pronged invasion of the British Province of Quebec.

Nathaniel Tracy outfitted the first privateers of the revolution. An extraordinarily wealthy man, he was owner of 120 vessels, 54 of these either privateers or cruisers. Beside his fleet, Tracy loaned $167,000 to the fledgling government. The war cost him his fortune. Both the frigates Hancock and Boston were built and equipped in Newbury.

President George Washington visits Newburyport in 1789, and the following year, lighthouses ceded to Federal Government. President George Washington appointed Abner Lowell as first Superintendent of lighthouses on Plum Island. The U.S. Revenue Cutter Massachusetts launched in 1791. Built by William Searle and when Alexander Hamilton was Secretary of the Treasury, she was the first such vessel in the service of the United States, thus allowing Newburyport to claim the birthplace of the U.S Coast Guard.

The War of Independence was disastrous to shipbuilding and trade. Independence destroyed the English market for ships and goods. The economic growth of the town was sharply curtailed. Private fortunes were lost, marking the end of an era.