As is the case with all legacy carriers in the United States today, 
United Airlines has a regional subsidiary, United Express, which serves regional routes across the country. These tend to be shorter than the airline’s mainline routes (with a few notable exceptions), and they are operated by smaller regional jets. Interestingly, these services are operated by subcontractors that United Airlines retains for these air services, each of which maintains its own dedicated fleet of regional jets to serve the United Express route network.