Hartman is a city in Johnson County, Arkansas, United States. The population was 519 at the 2010 census. Hartman is located in south…Hartman is a city in Johnson County, Arkansas, United States. The population was 519 at the 2010 census. Hartman is located in southwestern Johnson County on the west side of Horsehead Creek about 4 miles north of the Arkansas River. U.S. Highway 64 passes through the center of town, leading east 9 miles to Clarksville, the county seat, and west 13 miles to Ozark.