We stayed here on a trip out to Glacier NP. If you are just passing through to get from point A-B and don't want to get out into the back country, this campsite really fits the bill.
It's clean, maintained and relatively quiet. As others noted, it's essentially free, donations accepted.
This place is great and it runs off of donations, so make sure to drop some cash into their donation box if you can. Clean bathrooms and plenty of spots to park your car and camp, some with picnic tables even. There is trash and plastic/can recycling. Flush toilets and running water. There’s a shower at the civic center in town for $2, or one in Grass Lands for $5 just 30 min down the road.
This place is awesome. I wish they had these all over the country. Nice parking, covered picnic tables, Grassy and some shade, nice bathrooms. Free but please donate what you can so they will keep this open for the next time you pass thru.
The Lewistown Kiwanis provide a rest area and free campground to travels on the west end of town next to the airport. This camping area has no fee(they will take your donation to help with upkeep of the site), but does have restrooms with running water, several frost-frees are in the camping area to provide water, and trash cans are found at the restrooms. The camping area does not have numbered sites, but there are 12 concrete picnic tables, 6 of those are covered. No campfires at this campground. Their is plenty of room for camping even if all the tables are taken. Camping is limited to 10 nights. The airport is small so you will have very little aircraft noise, most noise will be from State Hwy 200/U.S. Hwy 87, but since the speed limit is 45mph noise from cars and trucks will be slight.