I am planning a week's vacation in mid- to late-September to Yellowstone National Park and the area with my husband and another couple. We will fly in from Raleigh, N.C. I would like recommendations about the best airport to fly into(Jackson, Denver or other), lodging, sights not to be missed and weather conditions that time of year. Will every thing be closed? Responses greatly appreciated.

Check out this link for a complete calendar of closures in September:

www.yellowstone-natl-park.com/cal.htm#Sep

and this one for things to do:

www.yellowstone-natl-park.com/plan.htm

We were at Yellowstone a couple of years ago in mid September. Most of the facilities were still open but I remember that some were closing the following weekend. We traveled down to the Tetons and took a float trip down the Snake River. The season for the company we went with was near an end. On the plus side, the crowds weren't bad. I've known people who visited in the summer and thought it was too crowded. The weather was beautiful - sunny and a little cool during the day, but quite cold at night.
We flew into Salt Lake City. The trip was about 5 hours. We had never been in this part of the country so we enjoyed the drive. I know Jackson Hole is very close, but we just could not justify the difference in price. We arrived in Salt Lake around 11:00 and drove through Idaho to West Yellowstone, MT the first night.

Jackson and Cody are the two closest airports.
If you can get to Yellowstone before mid-September, then you'll find most of the facilities still open. Also, the weather is a bit better and warmer. Still, you'll find the nights and early mornings to be cool.
We were there the day after Labor Day and it was near perfect. The autumn colors are beautiful and the wildlife is everywhere to be seen. (Note, however, that there was actually snow on September 10, which delayed our departure from Jackson for several hours!)

Thanks so much for the responses. We will take them into consideration as we plan our trip. If fact, if we can't go by mid-September, we may pick another place, such as the Grand Canyon and wait another year to go to Yellowstone.

We did the same thing last year from Greensboro. It was great. In fact, it was incredible. We flew into Jackson Hole. Rented a car and stayed at Signal Mountain Lodge. We hiked the Teton park area three days and then went up to Old Faithful Lodge and hiked in Yellowstone for three days. It was wonderful. Some gas stations in the park were closed but otherwise we found everything open, uncrowded and perfect for hiking. If you go to Signal Moutain Lodge, stop at Dornans on your way in and buy some trail mix. Good stuff. We enjoyed our meals there, too.

Bozeman is a great airport to fly into for Yellowstone and the drive down is through beautiful Gallatin Canyon. It's only about an hour drive.

I would say that the Bozeman airport is closer to Yellowstone and it is a fair size airport (more flight choices) compared to Jackson and Cody which are small, regional airports.

They have shuttles if you don't want a car but you really need a car for Yellowstone.

We are flying into West Yellowstone airport. We'll be there the last week of September.