Lowell is a city in Middlesex County, Massachusetts, in the United States. With an estimated population of 108,861 it is the fourth-largest city in Massachuetts, after Boston, Worcester, and Springfield, and the second-largest in what the U.S. Census Bureau defines as Boston's metropolitan area.

Incorporated in 1826, Lowell became known as the cradle of the American Industrial Revolution, and many of the city's historic sites have been preserved by the National Park Service. Lowell is home to the University of Massachusetts Lowell, a Carnegie-classified research university and the second largest public university in Massachusetts. Along with Cambridge, Lowell is one of Middlesex County's county seats.