Lowell is a city in Middlesex County, Massachusetts, USA. According to the 2010 census, the city's population was 106,519. It is the fourth largest city in the state. Lowell and Cambridge were the county seats of Middlesex County prior to the abolition of county government in 1997. Lowell is known as the cradle of the industrial revolution in the United States and many of the city's historic sites have been preserved by the National Park Service.