Mammoth Campground (Yellowstone)

July and August are peak season with 5,670 and 5,603 reservations respectively, and last-minute rates drop to 16.0% and 19.2% — meaning your odds of grabbing a site without advance planning are at their lowest. June and September offer a meaningful step down in competition while still delivering full wildlife activity and road access. May is the wild card: 92.7% of its 413 reservations were booked last-minute, making it the most accessible month in the dataset, though some campgrounds and facilities are still ramping up for the season.

Yellowstone has no internal shuttle system in the traditional sense — a personal vehicle is essential for moving between campgrounds and major attractions. Tower Fall and Slough Creek both require navigating the Grand Loop Road's north corridor, while Lewis Lake is accessed via the South Entrance road. Slough Creek adds a two-mile unpaved spur that limits larger rigs; plan your vehicle size before committing to a site there. Roads in the northern part of the park, including access to Mammoth, are generally open year-round, while most other campground access roads close in late fall.