Carroll County was formed in 1828 and named for Charles Carroll, the last surviving signer of the Declaration of Independence, who died in 1832. The county seat of Delphi was established the same year by General Samuel Milroy. The Wabash and Erie Canal, built through the county in 1840 and operating until the early 1870s, is among the county's most significant historical legacies.
The current Carroll County courthouse was designed by Elmer E. Dunlap of Indianapolis, who also designed the Spencer County courthouse. It was constructed by A. E. Kemmer at a cost of about $250,000 from 1916 to 1917. The exterior is understated, but the interior is surprisingly elaborate, including a stained glass dome over a mosaic tile floor.
This building is the county's third courthouse. The first was built in 1831-1838. It was replaced by a brick structure in 1856; this building was designed by M. J. McBird of Logansport and had a tower at each corner, including a clock tower. The 730-pound bell from the first courthouse was made in Cincinnati in 1836 and given by Sheriff Samuel Davis Gresham, and was used in the second courthouse until 1916. While the bell was in transit to Lafayette by boat, the boat sank; the bell was later recovered from the Ohio River. It was later sold, but was returned to Carroll County in 1967.