Homes for Sale in Rexburg Idaho: Rexburg is a city in Madison County, Idaho, United States. The population was 25,484 at the 2010 census, up from 17,257 in 2000. The city is the county seat of Madison County and its largest city. Rexburg is the principal city of the Rexburg, ID Micropolitan Statistical Area, which includes Fremont and Madison Counties. The city is home to Brigham Young University-Idaho (BYU-Idaho), a private institution operated by The Church of Jesus Christ of Latter-day Saints (LDS Church).