St. Deroin is a ghost town in Nemaha County, Nebraska, United States, originally located below the river bluffs on the Missouri River. Formally chartered in 1854, the town had a popular ferry crossing over the Missouri River for more than three decades. The river changed course, ending the ferry. After a railroad spur bypassed the town, it drew off more commerce. The community rebuilt its school on the river bluff when it was threatened by flooding; this area was also used for the cemetery. The town was completely abandoned by 1920, as flooding had destroyed much of the town-site. The site is at the northern edge of Indian Cave State Park.

Founded by "half-breeds" to serve the Nemaha Half-Breed Reservation, the town grew up around a trading post and was named in 1853 after Joseph Deroin (1819-1858), the trader. Deroin was the son of a Métis French Canadian trapper Amable Derouin and his Otoe wife. The elder Derouin had traded along the nearby Missouri River for decades, and a trading post was already operating near the townsite when Lewis and Clark came through with their expedition in 1804.

In 1840, Joseph Deroin set up a trading post along the river's edge at the mouth of the Platte River, at the main village of the Otoe. He married Meek-Ka-Ahu-me, an Omaha woman, and they had a daughter Mary. In 1842, Deroin also married the two Métis sisters, Julia and Susée Baskette (Bousquet), who were daughters of an Otoe woman; together he had a total of eight children with them. Joseph and his brother John Deroin each received allotments of land at the Nemaha Reservation, which was established in 1830. Joseph's daughter Mary and his third wife, Susée Baskette Deroin, also were recorded as having allotments there. Joseph was killed in 1858 by a white settler (husband of a Métis wife) in a dispute over money owed.