Colorado ranked fifth in the nation in voter turnout with 59.7 percent of eligible voters casting ballots. Montana came in tenth with a 56.6 percent voter turnout.
Anand Sokhey, associate professor of political science at the University of Colorado Boulder, said both states had ballot measures that people really cared about and competitive races.
"In Colorado you had a gubernatorial contest that people were enthusiastic about," he said.
Another factor that can lead to higher turnout is access to mail-in balloting, said Sokhey. This voting option is offered in both Colorado and Montana.
"I think that both states have done a pretty good job of making this a fairly easy process for voters," said Sokhey.
Voter turnout in Utah (40.8 percent) and Idaho (42.9 percent) was in the bottom ten in the country while Wyoming (48.4 percent) was slightly higher than the national average.