I will be visiting Yellowstone National Park, coming from Washington, DC. Which airport should I fly into?

West Yellowstone is closest, but Delta is the only airline that can get you there from here (I also am going to Y from DC), and they just cancelled my connecting flight from Salt Lake City. So, instead, I'm flying into Salt Lake and renting a car for the 5-hour drive. Other options are Jackson, WY (about 50 miles) and Cody (I think about 40 miles).

Another option is Bozeman Montana. Both Delta and Northwest fly into Bozeman which is approx. 60 miles from Yellowstone.
Have a great trip.

The West Yellowstone airport is very small and I don't know if commercial planes even fly into it. Try Bozeman (very easy) or Billings.

On our first trip to Wyoming, we flew into Cody and out of Jackson on United.

Don't forget that Pocatello and Idaho Falls are not that far out either.
From Salt Lake City, the driving distance is about 325 miles. I think you can make it in less than the estimated time from MapQuest. It is not a bad drive at all.

I take a longer route time wise because it is more scenic to come by way of Logan, with a drive through the canyon, and then north through the Tetons to get to Yellowstone. Takes longer of course. But if you are going to that area, the Tetons are a must also.

For price and ease would suggest Bozeman 90 miles from airport to park or from Billings which is further but have the opportunity of coming into the park by the not to be missed Beartooth Highway.

Your best bets are either Bozeman or Billings. And Photodog is right - the Beartooth Highway is one of the most scenic drives in the country. It takes about 4 hrs.
More direct is driving from Billings on the highway and then thru the Paradise Valley into Gardiner right on the edge of the Park- about 2.5- 3 hrs.
From Bozeman - you drive through the Gallatin Valley to West Yellowstone -- or up to Livingston and then thru the Paradise Valley to Gardiner.
Any of these is a beautiful drive.

America West flys to Billings from both IAD and DCA.
R5