The longest-lived president in American history has voted again.

Jimmy Carter, who turned 100 on Oct. 1 and has been in hospice care since February 2023, submitted his absentee ballot on Wednesday, according to Jason Carter, the former president’s grandson.

Jason Carter, the chairman of the Carter Center, said in a text message on Wednesday that his grandfather’s ballot had been deposited at a drop box at a local courthouse.

For weeks, according to the Carter family, the former president was privately playing down becoming a centenarian. Instead, Mr. Carter’s relatives said, he was most eager about voting for Vice President Kamala Harris.

Under Georgia law, Oct. 7 was the first day that county registrars could distribute domestic absentee ballots. Elections officials began mailing military and overseas ballots last month. Georgia’s in-person early voting period began on Tuesday, and regulators reported record turnout.

Elections officials said they were not certain when Mr. Carter, who spent many days of his post-presidency on Carter Center election-monitoring missions around the world, first cast a ballot of his own. But in 1943, Georgia became the first state to lower its voting age to 18; when Georgia voters decided to amend the state Constitution, Mr. Carter was months away from his 19th birthday.

Soon enough, though, he was in elected office himself. In 1962, he won a seat in the State Senate, after a chaotic scandal in which Mr. Carter’s opponent initially benefited from a ballot-stuffing scheme. (Decades later, Mr. Carter would recall that he was such an unknown then that a Georgia newspaper identified him as “Jerry Carter from Plains.”)

Mr. Carter cited the episode as a reason that he and his wife, Rosalynn Carter, who died last year, founded the Carter Center, a nongovernmental organization, after they left the White House in 1981. But before his defeat by Ronald Reagan, one of Mr. Carter’s earliest lobbying efforts as president focused on his ideas about voter registration and campaign finance.

State records show that Mr. Carter has been an especially reliable voter as a former president. He has routinely cast ballots in general elections, of course, but has also been a fixture of primary runoffs and special elections. For more than a decade, he has exclusively voted by mail in the elections tracked by the state.

Mr. Carter still lives in Plains — the tidy city in southwest Georgia that he turned into an outpost of presidential politics nearly a half-century ago — and votes in Sumter County, where plenty of people still know him as “Mr. Jimmy.” A Republican presidential nominee last carried Sumter in 2004, when George W. Bush won it by 126 votes.