Yellowstone is sold out.
Here's what to do.

Yellowstone receives over 4 million visitors per year. Most reservable campgrounds (Madison, Bridge Bay, Canyon, Grant Village) open reservations 6 months in advance on Recreation.gov and sell out within minutes for peak summer dates (July–August). Only Mammoth is open year-round; the others run May–September.

Pebble Creek and Slough Creek in the northeast corner are the easiest to book in Yellowstone — fewer visitors, small size, but spectacular wildlife access (Lamar Valley). Mammoth Campground is year-round and has more availability than summer-only sites. Check these before giving up on in-park camping.

West Yellowstone MT (west entrance) has several private campgrounds and RV parks within 5 miles of the gate. Gardiner MT (north entrance) is another option with private campgrounds and immediate availability. Both towns let you access the park daily without competing for in-park sites.

Recreation.gov releases cancellations daily at 7:00 AM Mountain time. Slough Creek and Pebble Creek see more cancellation activity than the big campgrounds because campers often rebook larger sites elsewhere. Set a CamperWatch alert for instant notification.

Indian Creek, Lewis Lake, and Tower Fall campgrounds are first-come, first-served and not reservable. They typically fill by 10–11am in peak season. Arrive the evening before for the best chance. Mammoth has a few first-come sites mixed in with its reservable spots.

Yellowstone does not currently require a vehicle timed-entry permit — unlike Glacier or Yosemite. You pay the entrance fee ($35/vehicle for 7 days) at the gate. Campground reservations are separate from park entry. This may change — check nps.gov/yell before your visit.