Petersburg is a city in Monroe County in the U.S. state of Michigan. The population was 1,146 at the 2010 census. Petersburg is named after Richard Peters, who sold the land necessary to found the town in 1836. It was originally called Summerfield and Peters was its first postmaster, but it was later named Petersburgh in honor of Peters and was eventually shortened to Petersburg. Petersburg is served by Summerfield Schools.