Ann Arbor is a city in and the county seat of Washtenaw County, Michigan, United States. The 2020 census recorded its population to be 123,851, making it the fifth-most populous city in Michigan. It is the principal city of the Ann Arbor metropolitan area, which encompasses all of Washtenaw County and had 372,258 residents in 2020. Ann Arbor is also included in the Metro Detroit combined statistical area and the Great Lakes megalopolis. Ann Arbor is home to the University of Michigan. The university significantly shapes Ann Arbor's economy as it employs about 30,000 workers, including about 12,000 in its medical center. The city's economy is also centered on high technology, with several companies drawn to the area by the university's research and development infrastructure. Ann Arbor was founded in 1824 by John Allen and Elisha Rumsey. It was named after the wives of the village's founders, both named Ann, and the stands of bur oak trees they found at the site of the town. The city's population grew at a rapid rate in the early to mid-20th century.