Mystic is a city in Appanoose County, Iowa, United States. The population was 322 at the time of the 2020 census. At the end of the 19th centur…Mystic is a city in Appanoose County, Iowa, United States. The population was 322 at the time of the 2020 census. At the end of the 19th century, "the valley of Walnut Creek was one continuous mining camp, known under different names, Jerome, Diamond, Mystic, Clarkdale, Rathbun and Darby". The present name is derived from Mystic, Connecticut. A. M. Elgin opened the first coal mine in the Mystic area in 1857, about 1.5 miles north of Mystic on Little Walnut Creek. The Mystic coal seam was exposed on the surface there, and drifts were opened and abandoned over the next few decades until the hills were honeycombed with mines.