McCaskill, whose name has been on a ballot consistently since 1982, said while heading into the polls that election day is always a "great day."
"The jury is deliberating, you've done all you can do, you try to take a deep breath and get rid of the nervous energy," McCaskill said.
Today, her campaign has 200 lawyers working throughout the state making working with voters to make sure there are no problems with voting.
McCaskill, who has a light public schedule today, said she would "check in with them and make sure they aren't seeing any concerns anywhere with accessibility."
Earlier in the morning, about five miles away in Ladue, Republican gubernatorial candidate Dave Spence was experiencing a different feeling: Tuesday marked the first time his name appeared on a General Election ballot.
"I think it is kind of surreal," Spence said. "It seemed when I started a year ago that this day would never come. And a lot of green beans and roast beef and chicken later, here we are. It exciting, and I'm excited for the opportunity."
When asked what it will take for him to win the election, Spence said he hopes voters will not split their tickets after checking the box for Republican presidential candidate Mitt Romney, who is expected to easily win the state.
Polls opened at 6 a.m. in Missouri, and close this evening at 7 p.m.