Matlock is a city in Sioux County, Iowa, United States. The population was 74 at the time of the 2020 census. Matlock is located at 43°14′35″N 9…Matlock is a city in Sioux County, Iowa, United States. The population was 74 at the time of the 2020 census. Matlock is located at 43°14′35″N 95°56′4″W / 43.24306°N 95.93444°W. According to the United States Census Bureau, the city has a total area of 0.37 square miles, all land.