Fly with Frontier. Save $30 Off!! Frontier is an American low-cost airline headquartered in Denver, Colorado. Its hub is located at Denver International Airport. Founded in 1994, it is a subsidiary airline of Indigo Partners. With a fleet size of more than 60 aircraft, Frontier Airlines flights cater to more than 50 destinations throughout the US and a few international destinations in Mexico, Puerto Rico, Jamaica and Dominican Republic. Some of its major destinations include Charlotte, Fort Lauderdale, Las Vegas, New York City, Philadelphia, San Francisco, Washington, D.C., San Juan, Punta Cana, Havana, etc.