Hardin is a city in southeast Ray County, Missouri, and part of the Kansas City metropolitan area within the United States. The population was 5…Hardin is a city in southeast Ray County, Missouri, and part of the Kansas City metropolitan area within the United States. The population was 571 at the 2020 census. Hardin was laid out in 1868. The community was named for Charles Henry Hardin, 22nd Governor of Missouri. A post office called Hardin has been in operation since 1858.