Lowell is a city in Massachusetts, United States. Alongside Cambridge, it is one of the two traditional seats of Middlesex County. With an estimated population of 115,554 in 2020, it was the fifth most populous city in Massachusetts as of the last census, and the third most populous in the Boston metropolitan statistical area. The city is also part of a smaller Massachusetts statistical area, called Greater Lowell, and of New England's Merrimack Valley region.