The National Park Service reports just over 640,000 people visited Yellowstone in September.
The visitation was down about 8.8 percent from September 2016, when the park recorded more than 700,000 recreational visits.
Snowy weather during the middle of last month closed some roads within and just outside the park for days.
Still, the Park Service says Yellowstone saw its third busiest September on record in the park.
So far this year, the park has hosted more than 3.8 million recreational visitors, down about 2.5 percent from the same period in 2016.