Calhoun County was formed on January 15, 1851 from open land originally named Fox County. It was renamed in 1853 after the seventh US Vice President secessionist John C. Calhoun. When the tracks of the
Illinois Central Railroad were laid through the county in 1870, the county seat was moved from Lake City to Rockwell City.
The first train reached Rockwell City on August 7, 1882 and the
population count doubled in the same year. The first courthouse, built
of wood, burned to the ground in 1884 and the county government moved
into a nearby hotel. In 1913, the current courthouse was built.
On July 6, 1893, Pomeroy was struck by a tornado that measured F5
on the Fujita scale. With a damage path 500 yards (460 m) wide and 55
miles (89 km) long, the tornado destroyed about 80% of the homes in
Pomeroy. The tornado killed 71 people and injured 200.