Concord, River, c.15 mi/24 km long, NE Mass., a short tributary of the Merrimack, which it joins at Lowell. On April 19, 1775, colonial militia fired some of the 1st shots of the Amer. Revolution at the British over a bridge across the river at Concord, Mass. Henry David Thoreau’s first book, A Week on the Concord and Merrimack Rivers (1849), records a boat trip with his brother. Concord Bridge is administered by the Natl. Park Service.
