Recount requested by Green Party candidate Stein in state where Trump beat Clinton by less than one percentage point.
The first candidate-driven statewide recount of a presidential election in 16 years began in Wisconsin, a state that Donald Trump won by less than a percentage point over Hillary Clinton after polls long predicted a Clinton victory.
The recount, requested by Green Party candidate Jill Stein, carries none of the drama of the Florida presidential recount of 2000, when the outcome of the election between Al Gore and George W Bush hung in the balance.
Stein, who made a $3.5m payment in recount costs this week, won about 1 percent of the vote in Wisconsin. She claims voting machines used in some parts of Wisconsin and other states are vulnerable to hacking and could have been manipulated.
"Verifying the vote through this recount is the only way to confirm that every vote has been counted securely and accurately and is not compromised by machine or human error, or by tampering or hacking," Stein said in a statement Thursday.
"The recount does not benefit one candidate over another. It benefits all voters across the political spectrum. This is an essential first step to restore confidence in our elections and trust in our democracy."
Almost no one expects Stein's push for recounts in Wisconsin, Michigan and Pennsylvania to result in a Clinton victory over Trump.
"This is certainly not Bush v Gore," said Wisconsin's chief elections administrator Mike Haas.
Even so, the campaigns for Trump, Clinton and Stein all had observers spread throughout the state to watch the recount.
In a Twitter post last week, Trump said Clinton, his Democrat rival, had already "conceded the election when she called" him before his victory speech in the early morning of November 9.
"So much time and money will be spent - same result! Sad," Trump tweeted, posting part of Clinton's speech telling her supporters to accept that "Donald Trump is going to be our president".
County election officials hired temporary workers, expanded hours and dusted off recount manuals to prepare for the work of retabulating nearly three million ballots.
Most counties will manually recount the ballots, although Stein lost a court challenge this week to force hand recounts everywhere.
The state's largest county, Milwaukee, was planning to recount the ballots by feeding them through the same machines that counted them on election night.
In Dane County, where Clinton won 71 percent of the vote, the ballots will be counted by hand.
Wisconsin election officials have less than two weeks to complete the recount.
December 13 is the federal deadline to certify the vote to avoid having the fate of Wisconsin's 10 electoral votes decided by Congress.
Even if that were to happen, the votes would almost certainly go to Trump, since Republicans control both chambers of Congress.