Hartwick is a city in Poweshiek County, Iowa, United States. The population was 92 at the time of the 2020 census. Hartwick is locate…Hartwick is a city in Poweshiek County, Iowa, United States. The population was 92 at the time of the 2020 census. Hartwick is located at 41°47′7″N 92°20′39″W / 41.78528°N 92.34417°W. According to the United States Census Bureau, the city has a total area of 0.13 square miles, all land.