Mountainburg is a city in Crawford County, Arkansas, United States. It is part of the Fort Smith, Arkansas-Oklahoma Metropolitan Statistical Area. The population was 682 at the 2000 census. Mountainburg lies along U.S. Route 71, and thrived when this road was the main route in northwest Arkansas. It is now a more sleepy community. The city park in downtown Mountainburg has since 1980 hosted two large dinosaur models.