Most travelers come to Montana in the summertime, when it’s easy to get around and towns are busy with events such as rodeos, powwows, and arts fairs. Even at the peak of the summer season, crowds usually aren’t a big problem. Even if there are a lot of tourists, there’s even more Montana.
Skiers, both downhill and cross-country, should definitely consider traveling here in the winter. Of course, that’s when the ski towns are in full swing, but there are many pleasures to be had from a quiet winter visit on cross-country skis or snowshoes to Glacier National Park [1].
Make note that fall is hunting season and that during the spring and early summer, many mountain roads and trails will still be blocked by snow.
Remember that Montana is a big state—it takes a good two days just to drive across it on the interstate—and allow yourself ample time to explore. A week will give you a good amount of time either to touch on a few areas of the state or to really explore one region.
Links:
[1] http://www.moon.com/destinations/montana/glacier-national-park