Frontier started its Denver flights on May 22 last year and concluded them on Oct. 27. It had originally planned to restart them on May 1 this year, HIA spokesman Scott Miller said.
However, Frontier advanced the startup due to available planes and the success of the route last summer, he said. Denver was the third most popular destination from HIA last summer, he said.
"It's amazing the ties we've found between the Harrisburg area and Denver," Miller said.
Most people are traveling the route for leisure reasons, such as visiting family or for vacation in Colorado, but there was some business travel, too, he said.
Frontier carried 49,052 passenger to and from HIA in 2012, or about 3.7 percent of the market share, according to airport statistics. In June, at the height of HIA's traffic in 2012, the airline was the fifth most popular with 7,436 total passengers.