The voting age was extended to 17-year-olds who will be 18 by the time of general elections.
Many candidates facing no opposition
The contest is considered crucial to the GOP’s efforts to regain control of the U.S. Senate.
Officials say they may not reach the 30 percent turnout they expected.
Nearly 500 have filed for Missouri offices so far.
Company that made the ballots said they tested them before sending them out to county clerks.