castalian springs is an unincorporated community and census-designated place (cdp) in sumner county, tennessee, united states. it is located along tennessee state route 25, about seven miles east of gallatin. the area has its own united states post office, designated by the zip code 37031. in the early 19th century, it was known locally as bledsoe's lick, and was the location of bledsoe's station, a fortified trading post. as of the 2010 census, its population was 556.