Waltham, a town of Middlesex co., Massachusetts, on the Charles river and the Fitchburg railroad, 10 m. W. by N. of Boston; pop. in 1850, 4,464; in 1860, 6,397; in 1870, 9,065; in 1875, 9,945. The most populous portion of the town is built principally on one street more than a mile long, and contains numerous fine residences. It is lighted with gas, and has water works recently erected and a good fire department. Waltham is extensively engaged in manufacturing. The chief establishments are the cotton cloth and hosiery factory and bleaching and dye works of the Boston manufacturing company, and the works of the American watch company, the most extensive in the world, and the first established (1854) for making.watches by machinery. Hollow ware, machinery, paper, cabinet ware, and boots and shoes are also produced. There are a national bank with a capital of $150,000, and a savings bank with $1,150,000 deposits. The assessed value of property is more than $10,000,000. The town contains a high school, two grammar schools, about 25 of lower grades, and a Swedenborgian theological school. The free public library contains nearly 8,000 volumes. Two weekly newspapers are published.

There are eight churches: Baptist, Congregational, Episcopal, Methodist, Roman Catholic, Swedenborgian, Unitarian, and Universalist. Waltham was separated from Watertown and incorporated in 1738.