Rolla is a city in, and the county seat of, Phelps County, Missouri, United States. Its population in the 2020 United States Census was 19,943. It is approximately midway between St. Louis and Springfield along I-44. Its micropolitan statistical area consists of Phelps County, Missouri. There is a nearby or overlapping is an inactive township. It is the home of the Missouri University of Science and Technology, well known for its many engineering departments and computer science department.