Calamus is a small town in Clinton County, Iowa, United States, located on the historical Lincoln Highway, which was the first transcontinental highway for automobiles across the U.S.. Calamus is the only town in Olive Township and had a population of 356 at the 2020 census, which was a 9.6% decrease from 2000. Calamus was named after Calamus Creek, which received its name from the great quantities of sweet flag growing in it, derived from the botanical name Acorus calamus, commonly called Sweet Flag or Calamus.

Clinton County is a county located in the U.S. state of Iowa. As of the 2020 census, the population was 46,460. Its county seat is Clinton. Its name is in honor of the seventh Governor of New York State, DeWitt Clinton.