Flight 2310 struck the bird shortly after leaving Seattle-Tacoma International Airport at around 3.36pm on Wednesday, but circled around and then landed again at 4.25pm, according to an airport spokesman.
The impact left a dent in the fuselage, but did not cause enough damage to put the aircraft in danger, the spokesman added.
The Port of Seattle said workers would send the animal's remains to the Smithsonian to determine what kind of bird it was, The Seattle Times reported.
Airline spokesman Ross Feinstein said the plane "landed safely and taxied to the gate".
He added: "Our maintenance team is currently evaluating the aircraft."
Passengers were transferred on to a different aircraft for the journey to Dallas-Fort Worth, Texas.
The pilot told air traffic controllers "looks like we hit some birds after takeoff, we're gonna need to go back and have the airplane looked at", ABC News reported.
The aircraft had 150 passengers and six crew on board.