Petersburg, MI has a population of 1,256 and is the 13,750th largest city in the United States. The population density is 2,602 per sq mi which is 2479% higher than the Michigan average and 2771% higher than the national average. The median age in Petersburg is 34 which is approximately 14% lower than the Michigan average of 40. In Petersburg, 54% of the population over 15 years of age are married, 100% speak English and 0% speak Spanish. 54% of Petersburg residents were born in Michigan, 45% were born out of state, 1% were born outside of the United States and 0% were foreign born.