washtenaw_county,_michigan | country | united_states <tsp> ann_arbor,_michigan | ispartof | washtenaw_county,_michigan <sep> washtenaw county ( wash-tə-naw) is a county located in the us state of michigan at the 2020 census, the population was 372,258 the county seat is ann arbor the county was authorized by legislation in 1822 and organized as a county in 1826 
ann arbor is located in washtenaw county. michigan in the united states of america.washtenaw county michigan is a u.s. state