Allegiant Air is adding 18 new routes and 10 new cities to its network.
The Las Vegas-based carrier says the expansion will bring its total number of destinations to 99, higher than any other US low-cost carrier's.
New to Allegiant's route map are two airports in the New York area: Long Island MacArthur Airport, which is east of the city, and Stewart International Airport, which is north of New York.
From 31 October, Allegiant will fly between Stewart and St Petersburg-Clearwater International. From 20 December, it will fly from MacArthur to Punta Gorda on Florida's southwest coast.
In the meantime, the airline will add services from Orlando Sanford International to a host of destinations: Concord, a northeast suburb of Charlotte, North Carolina; Bismarck in North Dakota; Charlottesville in Virginia; Clarksburg in West Virginia; Oklahoma City; Portsmouth in New Hampshire; Springfield in Illinois; St Cloud in Minnesota; and Tulsa, Oklahoma.
The carrier will also by year-end launch routes from St Petersburg to: Columbus in Ohio; Elmira in New York; Fargo in North Dakota; Sioux Falls in South Dakota; and Syracuse, New York.
In addition, Allegiant is to serve Fort Wayne, Indiana and Manhattan, Kansas from Phoenix-Mesa Gateway airport.