This is not the first time Colorado has used the caucus system, but there's still confusion among some voters who are new to the system.
Adams County clerk Karen Long says at least 100 people showed up at county offices by late Tuesday morning looking to cast ballots. Many people said they'd heard or seen radio or TV coverage about primaries happening across the country, and thought they could also vote in an election in Colorado.
About 300 other people called, asking where they could vote.
Long says it's confusing that Colorado is doing something different than other states are.
Caucuses are run by political parties, not counties, but the good news is voters still have time to get to the right place.
All Colorado caucuses take place Tuesday night.