I appreciate all the responses from all the folks who respond and share.
I am planning to visit YNP and the MT. Rushmore area in Sept. Yellowstone is pretty much committed to the end of Sept 2013 due to hotel reservations within the park ( I will spend a day or two in Grand Tetons). I just am not sure where to fly in and where to start first. Should I start in Mt. Rushmore area? I know weather may be a concern if I wait too late. I have two weeks to do all this so I do have a bit of time (haha-I really need 6 months) . I have to see both as I will never get my husband out here again. We will visit Custer state park, mt. rushmore, crazy horse and of corse the major area in YNP. The distances seem so far but we are okay with driving-just not the entire trip. I live in south florida so probably need to fly Delta or Southwest. Thanks again.

If you are going to start at Mount Rushmore then you need to fly into Rapid City, South Dakota. You can do that through Minneapolis-St. Paul if you use Delta but you could also do it through Denver.

For YNP and depending on how much driving you wish to do you could fly into Jackson, WY but sometimes that service is seasonal. You could fly into Billings. MT or even better into Bozeman (again on Delta)or just fly as far as Salt Lake and drive from there

Many Thanks

Might as well Include Jewel Cave, Wind Cave, and Badlands.

Buy a National Park Pass at your first entrance and save some $$$

Denver is 6 hours from Mt. Rushmore, and 9 hours from the center of Yellowstone. That's not a bad drive for someone with 2 weeks and likely will save a lot of money vs the smaller airports that are closer. You could add in a couple day stop at Rocky Mountain National Park is you fly into Denver.

I'd start at Denver because of the likely savings on air and car from the big hub.
I'd also add Cody, Beartooth Highway and a side trip to the Little Bighorn Battlefield.

For a price comparison, I would compare MSP to Denver for airfare and car rental combined. I have heard that it is quite expensive to rent a car in Denver (no personal experience).
Don't forget to see Devil's Tower on the way from Rapid City to Cody.

Denver is kind of expensive for rentals but you can work that price down if you work at it. I've usually saved about 40% by renting from downtown. Someone else on here got a great rate last summer by checking and checking every day.

MSP is over 9 hours from Mr Rushmore and 16 hours from Yellowstone. So they'd add about 10 hours of driving to get there and back. There are things to do along the way but the interstate in the Dakotas is not super exciting.

You'll have a great time and a great trip no matter what you do. Your only regret will be not having more time. But I digress...

Three suggestions:

1. Do not miss Devils Tower. A very cool, kind of spooky place. A thumb of basalt rising for no particular reason out in the middle of no-where.

3. To get to/from Devils Tower, take US 14 Alt from Spearfish, SD to Lead, SD. This 19-mile side road will take you through Spearfish Canyon. This is one of the under-rated, under-publicized gems of the American West. An absolutely gorgeous drive.

3. A general suggestion is to invest in a tripod and a camera with a delay timer. You'll want to use this to get pictures of your entire group in front of scenic vistas. I also like to use this setup to get pictures in front of road signs for the places I visit, and whenever I cross a state line.

Have a great trip.

We flew from FLL through SLC to Jackson Hole and then from Rapid City back to FLL on Delta miles, this was a few years ago. Flying into JH was easy an you are right in GTNP. We spent time in GT and Yellowstone and then drove through Cody to Devils tower and then into the Mt Rushmore area. The drive from Cody to Devils Tower was long and over the big horn mountains was unnerving for a Florida girl like me! We passed right by Devils Tower at night, I was spooked!! Too many years watching Close Encounters! Im so glad we had the experience of seeing it in the day as well as night! We also passed through Deadwood, just before the Sturgis Rally . Also great fun!! Wind Cave gets another vote, take a ranger led tour of the cave and see the amazing boxwork formations !!