The only commercial airline with regular service in and out of Niagara Falls, NY (IAG) is Allegiant. Spirit offers seasonal service as well, but according to their website they are not currently offering flights. IAG mostly serves private and cargo aircraft, as well as military flights for the Niagara Falls Air Reserve Station.
Just Allegiant and FedEx to my knowledge. It's a very small airport. For other airlines, you'll have to choose a bigger airport.
Allegiant currently flies out of Niagara Falls.
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