Newburg is a city in Phelps County, Missouri, United States. The population was 470 at the 2010 census. Newburg was founded in 18…Newburg is a city in Phelps County, Missouri, United States. The population was 470 at the 2010 census. Newburg was founded in 1883 by St. Louis – San Francisco Railway as a division point for the railroad, where engines would stop for repairs and to change crews. It is currently used heavily by the Burlington Northern Santa Fe Railroad as a maintenance stop, with a large supply of railroad materials along the double tracks.