Best Route from Rapid City, SD

I would be in no hurry to get up to US2 from Rapid City. We would take I-90 to Billings and then start working north using US87 to Great Falls and I-15 to Shelby and then US2 to Browning; or US89 from Great Falls to Browning. Once you get to Browning DO NOT take US89 from Browning to St. Mary unless you enjoy mountain driving. Take MT464 north out of Browning to where it intersects with US89 then turn south down to St Mary. Montana is not only Big Sky country it is just big, our fourth largest state. Enjoy your trip - the Black Hills and Glacier NP is two of our favorite areas.