Kentuckys Republican secretary of state, Michael Adams, said he hoped early voting and the large demand for mail-in ballots would avert long lines.
With the state now allowing any registered voter to vote by mail, more than 400,000 mail ballots were returned as of Sunday.
Counties have until eight days after Election Day to count and release the results of mail ballots, with 1.7 million requested by voters.
As Tuesday's voting approached, President Donald Trump continued his effort to undermine Americans' faith in mail-in voting by repeating his unfounded claim that the system is rife with fraud.
Because of MAIL-IN BALLOTS, 2020 will be the most RIGGED Election in our nations history - unless this stupidity is ended," he tweeted, accusing proponents of using Covid in order to cheat.Already this year, problems like long lines and lost mail-in ballots have plagued elections in Georgia, Nevada, Wisconsin and Pennsylvania.