Does anyone have a sense of the crowds at Yellowstone the week before Labor Day vs the week after Labor Day? I'd like to go the least crowded time possible, within this time frame. Thanks!

Provided that it doesn't snow (possible), the week after Labor day should have less people. Check to see if you can get reservations at either Old Faithful or at Mammoth. Do you plan to drive from home or take some form of public transportation?

Absolutely, after Labor Day.

Thanks for the input. We will be flying to Denver, then renting a car. I am remaining hopeful that we can fly by then!!

Sounds good. FYI: Salt Lake City is a little closer than Denver. Is there something you want to visit on the way from Denver to Yellowstone?

Yes, my daughter is moving to Laramie, WY so it will be a combination visit/NP trip!

Crowds after Labor Day maybe slightly less but don't count on an empty Yellowstone. With schools starting in mid/late -August the family crowds diminish by that time only to be replaced by the gray hairs and their RVs. A friend who seasonally worked Yellowstone was always surprised how quickly the grandparents replaced the grandkids with no down time. By October it will taper off.

An understatement. By late September it will likely have snowed which is the end of the season in Yellowstone, roads closed.

I am sorry MP but your knowledge of Yellowstone is lacking and your statement is plain wrong. Yes, it can/may snow in September BUT very unlikely. The average number of snow days in Sep is 1.1 days and average snowfall is 1.3 inches. Hardily enough to close Yellowstone. Sep is an excellent month in Yellowstone. Of course, that does not mean that they cannot have a big snow in Sep but the probability is extremely low. Our earliest snowfall in Denver is Sep 9th so, who knows, maybe the airport will be closed. I think you are safe to plan a Sep trip to Yellowstone.

We have always gone in September or October. Yes, in September things start to close down. In October we've been snowed on a bit. But I think early October is a good time to go, still. The crowds you do see will include many Asian tourists, as the golden week holiday is a popular travel time. Perhaps not so much this year, though, given the coronavirus situation.

Fmpden, wrong? I generally only post information of which I have personal knowledge, my trip to Yellowstone was in late September. Flurries, but nothing substantial the day we arrived. A week later at the end of the month a substantial snowfall brought road closures as we left the park. I was with a friend who has visited the park often throughout her life, a Montana native who has worked in the park and who said the timing was not unusual.

The time we spent in the park in September was simply great. Here is my trip report in several chapters that the OP may enjoy, if not everyone:
https://www.travelgumbo.com/blog/por...-s-yellowstone

The last sentence of the report above reads, "As we headed for the park’s northeast entrance, toward Red Lodge and Billings, the snow arrived and narrow winding Highway 212, the Beartooth Highway, closed behind us."

It's possible for the Beartooth Highway to close early for the season at the end of September. The Beartooth Pass reaches almost 11,000 ft in elevation and would normally close during the first half of October anyway. Closures of roads within Yellowstone in late September would be temporary as most roads are scheduled to remain open until early November with the northern road from Gardiner to Cooke City maintained year round. Most of our trips have also been in fall and we've stayed as late as early November though the weather does get increasingly volatile into October. It's always wise to be prepared for snow but September isn't the end of the season.

I stand corrected. Thanks Patty.