A Barrett spokesman said the campaign was not conceding, citing voting under way in Milwaukee, Madison and Racine.
"We feel very confident when those come in, Tom Barrett is going to win," Phil Walzak said.
Democrats and organized labor spent millions to oust Walker, but found themselves hopelessly outspent by Republicans from across the country who donated record-setting sums to Walker. Republicans hope the victory carries over into November and that their get-out-the-vote effort can help Mitt Romney become the first GOP nominee to carry the state since Ronald Reagan in 1984.
The recall was a rematch of the 2010 governor's race. Throughout the campaign, Walker maintained his policies set the state on the right economic track. Defeat, he said, would keep other politicians from undertaking such bold moves in the future.
"We're headed in the right direction," Walker said many times. "We're turning things around. We're moving Wisconsin forward."
Barrett repeatedly accused Walker of neglecting the needs of the state in the interests of furthering his own political career by making Wisconsin "the tea party capital of the country." He said Walker had instigated a political civil war in Wisconsin that could be quelled only by a change in leadership.
"I will end this civil war," Barrett promised in a debate. "That is something the people of this state want."
Walker ascended into the national spotlight last year when he surprised the state and unveiled plans to plug a $3.6 billion budget shortfall in part by taking away the union rights of most public workers and requiring them to pay more for their health insurance and pension benefits.
Democrats and labor leaders saw it as a political tactic designed to gut the power of his political opposition. State Senate Democrats left Wisconsin for three weeks in a sort of filibuster, as tens of thousands of teachers, state workers and others rallied at the Capitol in protest.
But the tea-party supported fiscal conservative remained steadfast: Walker believed his plan would help him control the state budget, and his opponents could not stop Republicans who control the state legislature from approving his plans.
Walker went on to sign into law several other measures that fueled calls for a recall, including repealing a law giving discrimination victims more ways to sue for damages, making deep cuts to public schools and higher education, and requiring voters to show photo ID at the polls.
Both sides mobilized thousands of people and millions of dollars to influence voters, whom polls showed were more divided than ever. Signs calling for Walker's removal and those supporting the 44-year-old son of a minister dotted the state's landscape all spring at a time normally devoid of political contests.
Turnout was strong across the state with few problems reported as some voters waited in line to cast their ballots.
"Typically we wait until 5 in the afternoon, but we were chomping at the bit to just get it over and done with because I think it has been an unjust campaign waged against the governor," said Jeff Naunheim, a warranty analyst from St. Francis who voted for Walker first thing Tuesday.
Naunheim said the recall was a waste of money.
"I think the Wisconsin voters voted in 2010 to vote Walker in," he said. "I don't think he did anything illegal."
Barrett supporter Lisa Switzer of Sun Prairie said Walker went too far.
"Even if it doesn't turn out the way we want it to, it proves a point," said Switzer, an occupational therapist and single mother on BadgerCare, the state's health insurance program for the working poor. "People in Wisconsin aren't just going to stand by and let a governor take over the state and cut social services."
More than $66 million was spent on the race as of May 21, making it easily the most expensive in Wisconsin history. That money was spent on an all-out barrage of television ads, direct mail, automated calls, and other advertising that permeated the state for months.
Walker used the recall to raise millions from conservative donors and bolster his own political fame in the face of the fight.