There is a population of wild horses in Montana. In fact, one town in Montana is named for them. The town is usually known as Plains, Montana but the full name of the town is Wild Horse Plains. The town is located in a river valley in Northwest Montana.
The population of wild horses in Montana has never been large and wild horses aren’t often seen, though there is still a population.
There are many in Utah I have seen.
I don’t think anyone knows for sure how many there are in Montana.