Santa Claus is a town in Spencer County, Indiana, United States, in the southwestern part of the state. Located in Carter, Clay and Harrison Townships, it sits between Interstate 64 and the Ohio River. The population was 2,481 at the 2010 census, making it the largest community in Spencer County.The town was established in 1854 and known as Santa Fe. In 1856, when the town was working to establish a post office, the United States Postal Service refused their first application as there was already a Santa Fe, Indiana established with the USPS. Several town meetings were held, during which the name Santa Claus was selected.The town has the world's only post office to bear the name of Santa Claus. Because of this popular name, the post office receives thousands of letters to Santa from all over the world each year. A group of volunteers known as Santa's Elves ensures each child receives a reply from Santa Claus; this tradition has been in existence since at least 1914.