Moose Creek Flat Campground

Stayed here in mid-July, 2020. Could only snag 4 nights here as all sites are by reservation only. A beautiful setting with the roaring river on one side (luckily we were able to get one of those spots) and sheer cliffs on the other and tall pines everywhere (not in the campground). The west side of the campground has all sites which back-in to the river, while the south end and east side (which is next to Highway 191) are pull thru sites. All sites here can accommodate large rigs and access from the Highway and inside the campground is a snap. No hookups here and there are pit toilets and trash receptacles available.
We really liked this camp. There is plenty of room to stretch out, as all the sites are huge. The roaring river was awesome. We took our camp chairs about 20 feet from behind our site to sit right next to the river. It is also convenient to the hipster town of Big Sky to the south and Bozeman to the north. Both make great day trips and offer lots of activities, eating and shopping.
Granted, the highway is noisy most of the day. You knew it was time to get up when the traffic started up again about 7:30AM or so, after a relatively quiet night. Quiet, that is, except for the river, if you are camped on that side. No cell phone signal here at all. We travelled to Big Sky for that.
Would love to return here someday, IF we can get a reservation.

I understand the negative comments about the highway noise, but in practicality, it is a very narrow valley with very few places to camp. We really enjoyed it here. We were fortunate to have one of the riverfront spots, and admittedly, it made a big difference. My opinion would vary greatly if I had stayed in one of the pull-through sites that border the highway. The river "music" nicely counterbalanced any road noise.
This is dry-camping, with no internet or phone service at all. Big Sky is close by to access anything you need. Very big spaces, but it really didn't matter. We almost had the campground to ourselves in late June. There is a large parking lot at the north end where the rafts pull out, so it can get a little busy there. We really enjoyed it here and will hopefully be able to stay again.
My only hint... negative comment, is that the signage is POOR. There is no sign coming from the south and a very quick one from the north. Traffic does travel quickly through here and it made for some stressful moments figuring out where we were going.

Mid July, we found a walk up site for one night. Spacious sights with a river running behind. We leave our windows open at night when it's chilly and it was extremely loud. I'm a sound sleeper and it woke me up several times. There are no hookups here, but there are toilets, water fill up, and garbage on site. We wouldn't stay here again because of the noise. Also, no att cell service.

Small campground sandwiched between the Gallatin River and the road. All sites are in full sun, which worked for us because of our solar panels, but it did get very hot in the afternoon sun. We were lucky enough to grab site #9 which was a walk in site and probably the nicest one, because it is parallel to the river and thus gets shade from the trees in the afternoon. Some sites are walk in and some you can reserve online. There is no park host at this site (they are down the road at Greek Creek) but you just need to look at the tags to determine if a site is open. All the sites back up to the river unless you choose one of the three pull through sites, which back up to the road. Sites 6-8 back up to a really nice beach. There is also public water access and picnic area that has a beach as well. Amenities include two pit toilets and hand pump water spigot!
The Gallatin River is a beautiful and cold river that balanced out the hot sunny spot. There are many people fishing and rafting on the river. The road is very heavily travelled by commuters, tourists and commercial trucks. Even though the road noise did not abate at night the sound of the river (at our site) helped make it tolerable. Big Sky was about a 10-15 minute drive and cell reception came through there (there was no signal in the valley) or you could drive towards Four Corners/Bozeman and get service there, but it is a longer drive.

It wasn't a bad place to be stuck while our transmission was rebuilt!