I am thinking of visiting Yellowstone and Grand Teton in September or October by myself. Are there enough hikes that I can safely do alone? I’ve heard of some hikes in bear country requiring groups of four or more. Human predators are also something to consider. I’m wondering if there are still plenty of people around in general that time of year out on the trails.

All of Yellowstone and Grand Teton is bear country. We've been in late September/early October and trails were fairly quiet. We only ran into other hikers sporadically. There are two of us and we both carry bear spray and make noise. It can snow at that time of year as well.

> I’ve heard of some hikes in bear country requiring groups of four or more.

You heard wrong.
https://www.nps.gov/yell/planyourvis...ar-country.htm
While it is a SUGGESTION that you not hike alone in areas where grizzlies are active, it is not REQUIRED.
And the number is three, not four.
There are areas that are closed to ALL hiking due to aggressive grizzlies, but these are clearly marked.
Discuss what you would like to experience with the rangers, and they will assist you in finding hikes that are safer than others.
Note that there is NO hike in Yellowstone that is 100% safe -- which is part of the experience.

I also strongly urge you to carry bear spray on any solo hike in this area. I don't carry it when I hike solo in the East, despite having seen black bears on six different occasions. But grizzles are a COMPLETELY different species!

Go to the official NP site for Yellowstone and GT and look for what is offered for ranger led hikes at the time you will be there to be safe. There are plenty of short hikes with other people around in Yellowstone if you stick fairly close to the loop roads.

Here's last September's ranger programs YT17_Fall_Programs_web.pdf Very little is offered in October.

Grand Teton ranger programs https://www.nps.gov/grte/planyourvis...P_JUMP_2381476

You may also be able to find some guided hikes through the Yellowstone Institute https://www.yellowstone.org/experien...ver-institute/ Again very few of these will continue into October.

We were there from September 30th to October 7th last year. The geothermal areas, canyon, waterfalls, etc attract the most people. Outside of those areas we encountered few other hikers even on short trails. On one hike (Lost Lake trail behind Roosevelt Lodge) we didn't run into anyone else.

Oh for heavens sake--I hike by myself--all.the.time. Yes, carry bear spray--that is smart. Yes, you have more to fear from people than bears. But go!!! You will have a great time! That time of year tends to attract retired folks vs. young families but they hike too!! September is a truly magical time. Go at the end of Sept--not too hot or too cold. You will have a great time.

Thank you Patty, Paul and enalloy.

I've done the road trip to Yellowstone and GTNP alone as a single woman with no problems. If you can go the first couple weeks in September, the weather should be wonderful and there will still be other people on the trails. When I was there in 2011, there had been a couple casualties by grizzlies attacks in the prior month which did cause me some concern and probably an added level of caution but I took grizzly spray, checked out ranger led hikes and asked strangers if I could join them on their hike. The last option was a great opportunity to meet other travelers and was my favorite option. Go, you're going to love it. Oh, and if you want one more protection, carry a bell. But then you're probably more likely to be attacked by a human driven crazy by that darn bell!

I worked in Yellowstone for a summer and have driven the Yellowstone/GTNP loop many times by myself. In the late 80s/early 90s I even picked up 2 backpackers hitchhiking. (because I hitchhiked with my friends to get from trailhead to trailhead when I worked there)

I do carry a sheep bell when I backpack in bear country. It's light weight--like a small cow bell but can be heard. I have had people complain that they could hear it a mile away--good, then the bears can hear it too! And I have never seen a grizzly while hiking/backpacking. I have seen black bears in the east coast--but I wasn't carrying my bell!