Resident Population in Washtenaw County, MI was 365.53600 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Washtenaw County, MI reached a record high of 371.81700 in January of 2020 and a record low of 234.10300 in January of 1970. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Washtenaw County, MI - last updated from the United States Federal Reserve on May of 2024.