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 439 at the 2010 census, which was an 11.4% increase from the 2000 census. 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.