Henning is a city in Otter Tail County, Minnesota, United States. The population was 854 at the 2020 census. Henning was incorporated i…Henning is a city in Otter Tail County, Minnesota, United States. The population was 854 at the 2020 census. Henning was incorporated in 1887, and named for John O. Henning, a pharmacist. According to the United States Census Bureau, the city has a total area of 3.38 square miles, of which 3.34 square miles is land and 0.04 square miles is water.