Originally known as Aspinock and then part of Killingly, Putnam was incorporated in 1855 from parts of Killingly, Pomfret, and Thompson and was named for Revolutionary War General Israel Putnam. Some of its early settlers helped lead expansion to the Northwest Territory in 1787. One of the first cotton mills in the country was built there in 1806, and with waterpower and the opening of the railroad in 1840, textile industries flourished. After the mill district was devastated by the flood of 1955, Putnam's industrial area was rebuilt.