In August 2017, Allegiant announced a new base would be established at the Indianapolis International Airport. The base began operations in early 2018. In February 2018, Allegiant also announced a new base would be established at the Destin–Fort Walton Beach Airport. In June 2018, Allegiant added another base at McGhee Tyson Airport in Knoxville, Tennessee. In January 2019, Allegiant announced they would be adding another base at Gerald R. Ford International Airport in Grand Rapids, Michigan.
In May 2005, the airline's holding company, Allegiant Travel, completed a private equity placement worth $39.5 million that was funded by the investment firms of ComVest and Irelandia II. In November 2006, Allegiant filed a registration statement with the Securities and Exchange Commission in anticipation of a planned initial public offering of its Common Stock. It raised $94.5 million in equity capital with 5.75 million shares worth $18 each. It began trading on the NASDAQ Stock Market under the ticker symbol "ALGT" in December 2006.
The initial JetExpress partnership with Mesa ended in January 2004, when Horizon Air was selected to operate the routes. Horizon utilized slightly larger CRJ-700 regional jet aircraft on these routes. In August 2006, Frontier and Horizon ended their partnership. While Frontier was generally pleased with Horizon's operation, the carrier decided that it needed to revisit the agreement and find a provider with additional regional jets to grow the operation. The last of the CRJ-700's was returned to the Horizon Air fleet on November 30, 2007.