Petersburg is a city in western Monroe County, Michigan. Originally founded as Summerfield, it is located in the northern potion of Summerfield Township. The community is located about five miles south-southwest of Dundee and seventeen miles west of Monroe. The population was 1,157 during the 2000 census. According to the United States Census Bureau, Petersburg has a total area of 0.5 square miles. The community uses ZIP codes 49720—assigned to Petersburg— and the city has the FIPS code 26-63800.