High Quality Content by WIKIPEDIA articles! Ann Arbor is a city in the U.S. state of Michigan and the county seat of Washtenaw County. The 2010 census places the population at 113,934, making it the sixth largest city in Michigan. The Ann Arbor Metropolitan Statistical Area (MSA) had a population of 344,791 as of 2010. The city is also part of the larger Detroit – Ann Arbor – Flint, MI CSA.