Harlan Township is one of twenty townships in Fayette County, Iowa. As of the 2010 census, its population was 871.
According to the United States Census Bureau, Harlan Township covers an area of 36.79 square miles (95.28 square kilometers); of this, 36.76 square miles (95.22 square kilometers, 99.94 percent) is land and 0.03 square miles (0.07 square kilometers, 0.07 percent) is water.
The township contains these two cemeteries: Hope and Long Grove.