April, early May.
Where do you want to go and what do you want to see to renew your roots? Glacier Park in the NW and Yellowstone in the SW are always big attractions but openings depend on the snow levels. Others include the Little Big Horn Battlefield site and various marker sites along the trail followed by Lewis & Clark on their way west, Fort Benton and Great Falls (near where L & C found the Great Falls of the Missouri River). The Charlie Russell Museum is in Great Falls. Russell was Montana's "cowboy artist" and was friend to the late great Will Rogers. The main university towns of Bozeman & Missoula are great, with lots of liberal spots and activities. Missoula also hosts the tiny but staunchly pacifist Jeannette Rankin Peace Center and the wonderful Maureen and Mike Mansfield Foundation, created to promote understanding among peoples of Asia and the US. Helena is famous for Last Chance Gulch where the big gamble paid off and gold was discovered. Flathead Lake, with its valley and the beautiful Mission Mountain range, is lovely and nearby Bigfork is an arts center. The Confederated Tribes (Flathead, Salish, Kootenai) reservation is on the way to Flathead Lake.
The emphasis, as you may remember, is primarily on outdoor and sporting activities and there are lots of little jewels than can be discovered. Check out for example, the range of B&Bs in the state, a great way to meet people. Two I can recommend heartily are the Stone School Inn in Valier and the Great Northern Bed and Breakfast in Chester, where the lovely Patty Aaberg and her husband, New Age musician Phil, host. Both Patty and Phil are longtime family friends. My mother actually taught at the Stone School Inn during WWII when it was still a working school. Another jewel is the Isaac Walton Inn falling midway between East and West Glacier on US#2, originally built to house the train crews who had to operate the engines to assist the trains over the Continental Divide.
These are just a few places off the top of my head and there are lots, lots more. MT is purple, rather than red, independent rather than R, like many of the western States. There are lots of good Dems there, some very liberal, some more centrist. Unfortunately, due to some very unpopular USSC decisions, corporate money from outside the state is pumped in to support very conservative R candidates, which is why a total zilch such as comparative outsider Steve Daines won the Senate race in 2014. Those same elements are pouring money into the gubernatorial race this year and I hope that people are not duped again.
Sorry for the essay - didn't mean to ramble on so much. But MT is my birth state and I still love it and those I know who live there. I'll be there myself for about a week later this month and am looking forward to that.