Yellowstone probably should be a trip unto itself. Way too much to cover in a couple of days I'm sure.
This link will help you with opening and closing dates of various park campgrounds, facilities and other features.
Plan your visitThe park is open for a very short time during the year, with some areas not opening till June 15 and virtually everything closed by September 15. Not much of a window to cram a zillion people into.
The park has a number of campgrounds that are first come first serve, operated by the NPS, and others operated by a contractor, Xanterra, who require reservations.
Here is a slightly different list, with the same info you will find several different places on the net.
Sorry, I am not able to get the links to carry over when I copy this. Will try to do so as it is a lot of info in one place.
GATEWAY COMMUNITIES
Cody, Wyoming (east entrance)
Cooke City, Montana (northeast entrance)
Gardiner, Montana (north entrance)
Jackson Hole, Wyoming (via Grand Teton National Park) (south entrance)
West Yellowstone, Montana (west entrance)
YELLOWSTONE NATIONAL PARK
Facilities in Yellowstone open and close on a staggered basis. The dates listed are always subject to change due to weather conditions. Links are provided whenever possible to give you more information and to double check on the opening or closing date.
Lodging inside Yellowstone is handled by Xanterra. Many find it cheapest to make reservations directly with them, through their website or by calling directly (307-344-3711).
OPEN YEAR ROUND
Albright Visitor Center in Mammoth – this link also takes you to information on the other visitor centers in Yellowstone.
Mammoth Campground – First come, first served – no reservations – Live view of what’s available.
The road from the North Entrance at Gardiner, Montana, through the park to Cooke City, Montana, via Tower Junction is open twenty-four hours a day, all year to auto travel, but is closed to the east of Cooke City.
SUMMER 2017
OPENING DAY April 21:
ROADS – Mammoth to Old Faithful; Madison to West Entrance; Norris to Canyon.
Geyser Grill (in the Old Faithful Snow Lodge) opens at 11 am.
Bear Den Gift Store (in the Old Faithful Snow Lodge) opens at 11 am.
APRIL 28:
Mammoth Hot Springs Hotel and cabins opens at 11 am.
Terrace Grill (in Mammoth) opens at 11 am.
Old Faithful Snow Lodge opens at 11 am.
Madison Campground opens.
MAY 5:
ROADS – Canyon Junction to Lake; Lake to East Entrance (Sylvan Pass).
Old Faithful Inn opens at 11 am.
Fishing Bridge RV Park estimated opening day. Takes reservations.
MAY 12:
ROADS – Lake to South Entrance; Tower Junction to Tower Fall.
Lake Yellowstone Hotel and Cabins open at 11 am.
Lake Hotel Deli opens at 11 am.
May 19:
Norris Campground opens. First come, first served – no reservations. Live view of openings.
Tower Fall Campground opens. First come, first served – no reservations. Live view of openings.
Bridge Bay Campground estimated opening day. Takes reservations.
Old Faithful Lodge opens at 11 am.
Bake Shop & Gift Store (in the Old Faithful Lodge) opens at 11 am.
Grant Village opens at 11 am.
MAY 26:
ROADS – Tower Fall to Canyon Junction (Dunraven Pass); Beartooth Highway.
Lake House restaurant (at Grant) opens at 11 am.
Canyon Campground estimated opening day. Takes reservations.
JUNE 2:
Canyon Lodge and Cabins open at 11 am.
Canyon Cafeteria, Dining Room and Gift Store open at 11 am.
JUNE 9:
Roosevelt Lodge and Cabins open at 11 am.
Indian Creek Campground opens. First come, first served – no reservations. Live view of openings.
Grant Village Campground estimated opening day. Takes reservations.
JUNE 10:
Lake Lodge and Cabins open at 11 am.
Lake Lodge Cafeteria opens at 11 am.
JUNE 15:
Pebble Creek Campground opens. First come, first served – no reservations. Live view of openings.
Slough Creek Campground opens. First come, first served – no reservations. Live view of openings.
Lewis Lake Campground opens. First come, first served – no reservations. Live view of openings.
JUNE 15 – SEPTEMBER 4: ALL FACILITIES OPEN
SEPT 4:
Roosevelt Lodge and Cabins closes at 11 am.
SEPT 11:
Bridge Bay Campground closes at 11 am. Takes reservations.
Indian Creek Campground closes. First come, first served. No reservations. Live view of openings.
SEPT 17:
Grant Village Campground closes at 11 am. Takes reservations.
Fishing Bridge RV Park closes at 11 am. Takes reservations.
SEPT 24:
Canyon Campground closes at 11 am. Takes reservations.
Lake House restaurant (at Grant) closes at 11 am.
Lake Lodge and Cabins close at 11 am.
Lake Lodge Cafeteria closes at 11 am.
SEPT 25:
Norris Campground closes. First come, first served – no reservations. Live view of openings.
Tower Fall Campground closes. First come, first served – no reservations. Live view of openings.
Pebble Creek Campground closes. First come, first served – no reservations. Live view of openings.
OCT 1:
Grant Village closes at 11 am.
Old Faithful Lodge Cabins closes at 11 am.
Bake Shop & Gift Store (in the Old Faithful Lodge) close at 11 am.
OCT 8:
Lake Yellowstone Hotel and Cabins close at 11 am.
Lake Hotel Deli closes at 11 am.
Old Faithful Inn closes at 11 am.
Canyon Lodge and Cabins close at 11 am.
Canyon Deli and Gift Store closes at 11 am.
OCT 9:
Mammoth Hotel and Cabins close at 11 am.
OCT 15:
Madison Campground closes at 11 am. Takes reservations.
Terrace Grill (at Mammoth) closes at 11 am.
OCT 22:
Old Faithful Snow Lodge closes at 11 am.
NOV 5:
Lewis Lake Campground closes. First come, first served – no reservations. Live view of openings.
Geyser Grill (in the Old Faithful Snow Lodge) closes at 11 am.
Bear Den Gift Store (in the Old Faithful Snow Lodge) closes at 11 am.