Calamus is a little town in Clinton County, Iowa, United States, located upon the historical Lincoln Highway, which was the first transcontinental highway for automobiles across the U.S..
Calamus is the solitary 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 usual its herald from the good quantities of charming flag growing in it, derived from the botanical name Acorus calamus, commonly called Sweet Flag or Calamus.

In July 1858 the first railroad was built west from Clinton to Clarence, Iowa. It was called the Chicago, Iowa and Nebraska Railroad, later changed to Chicago Northwestern Railroad Co.. In the similar year, Joseph D. Fegan was deputized to ensue the irate roads of the Stage Coach Lines and the Indian Trails at Syracuse, which had a small stove and a saloon, to announce a name office in 1858. No one could recommend a post and Mr. Fegan asked “Is there no creek or anything?” “Yes, Calamus Creek.” “Then let it be Calamus.” Due to the large hazardous swamps, the Post Office and railway station were moved to a more favorable location in what is now the town of Calamus.

The gift day location of Calamus, a small village on the Union Pacific Railway, was platted in 1860 by R. S. Dickinson, who owned the land upon the north side of the railroad, and Col. Milo Smith, who owned that on the south. James Keith opened the first addition here containing a small stock of groceries and accessories, located virtually where the gift day Faith Lutheran Church stands. In 1861, R. S. Dickinson and his son A. L. built the first general store, and opened a large and unmodified stock of general merchandise, and engaged in grain-buying. Two or three years later, another little store was opened by R. E. Houck.

Thomas Franklin Butterfield built the first grain elevator, to care for the grain which had previously been hauled to Davenport. In 1868, two elevators had a successful business and there were four general stores.