Carroll County was formed on January 15, 1851 from sections of Pottawattamie County. It was named after Charles Carroll of Carrollton, Maryland, the only Roman Catholic and longest-living signer of the Declaration of Independence. In 1855, the county government was established in Carrolton and in 1858, the first courthouse was built. In 1869, the seat was moved to Carroll City (today Carroll) which was centrally located and connected to the Chicago and North Western Transportation Company. The courthouse was destroyed in 1886 by fire. The present courthouse was erected in 1965. However the courthouse is set to go under construction in the near future.