Toleno gained 352 votes to O'Connor's 323, capping a vigorous campaign that included both candidates seeking to knock on the door of every home in the district.
"I'm thrilled," Toleno said Tuesday night, adding that he believes voters responded to his work for community groups and as a Brattleboro businessman.
"People saw me as somebody who'd made a commitment to the community in a number of ways," Toleno said.
O'Connor said she would not challenge the result. She suffered a defeat in her first run for office after years working in state and national politics.
"I've been in this business a long time. In politics, there's always a surprise right around the corner," O'Connor said. "The biggest lesson you learn is, you win some and you lose some."
No other candidates had entered the primary race for a House seat that Progressive Sarah Edwards held for a decade. Edwards declined to seek another term.
The campaign had pitted O'Connor's political experience against Toleno's experience in business and community activism.
O'Connor got her start with the 1988 campaign of Vermont Gov. Madeleine Kunin and was a longtime aide to former Gov. Howard Dean. O'Connor also was involved in Dean's unsuccessful bid for the Democratic presidential nomination in 2004.
"I have a relationship with the governor. I think that really benefits Brattleboro," she said in the run-up to Tuesday's election. "I'm not going up there an unknown entity."
Toleno, though, said his experience also should count: His community activities include Brattleboro Civilian Police Communications Committee, Brattleboro Area Chamber of Commerce, Landmark Trust (Scott Farm) treasurer, Healthy Communities Coalition and Sunrise Rotary.
He is a well-known Brattleboro businessman: Toleno operated the former Riverview Cafe and now runs Entera Catering.
Toleno also professed a deep interest in public policy and food systems; in a recent interview, he talked about furthering Vermont's efforts to create a "vibrant agricultural economy."
Edwards had endorsed Toleno, citing his energy and enthusiasm as well as his "roots, connections and commitment to our community."
O'Connor had received Dean's endorsement. But she also had to answer persistent questions about her involvement in the unsuccessful 2006 U.S. Senate campaign of Republican Richard Tarrant.
O'Connor said she was an adviser, not a top official, in Tarrant's campaign and simply was responding to the candidate's request for input from a Democrat.
"The negativity - it was too bad that it got that way," O'Connor said after the votes were tallied Tuesday. "The last two weeks have been tough - very tough."
Toleno said his campaign was not the source of that negativity.
"I don't have control over other peoples' opinions," he said.
MONTPELIER -- Windsor businessman John MacGovern handily defeated a Republican primary opponent in the race to challenge Vermont's independent U.S. Sen. Bernie Sanders in November.
With 34 percent of the precincts reporting, MacGovern led his opponent Brooke Paige by 50 percentage points. MacGovern had 75 percent of the votes cast while Paige had 25 percent.
By about 9 p.m. in the Democratic attorney general's race, incumbent William Sorrell led challenger T.J. Donovan 52 percent to 48 percent.
Secretary of State Jim Condos estimated between 8 and 10 percent of Vermont's 446,000 registered voters would go to the polls. He attributed the sparse interest in the primary to the lack of high-profile contests.
"In all reality the top of the ticket is where the action would be," Condos said.
The race that has drawn the most outside interest is the Democratic race for attorney general, which pits Donovan, the Chittenden County State's attorney, against incumbent Sorrell.
The attorney general race is the only contest that has generated any significant campaigning, with both sides crisscrossing the state and accumulating endorsements from other politicians and newspapers.
Donovan has criticized Sorrell on several fronts, including a charge that the incumbent hasn't done a good enough job working with the Legislature to pass strong laws that will hold up in court. Sorrell points to what he claims is a strong record defending the state.
Despite the light turnout, some voters were committed to casting their ballots.
"I vote every time I can and put my foot into the system, even a small foot," said Georgette Putzel, of Jericho, who spoke after leaving Montpelier City Hall, where she had attended a meeting. She said she planned to vote for Sorrell.
MONTPELIER -- The race for the Democratic nomination for Vermont attorney general is too close to call.
With 95 percent of the precincts reporting, incumbent William Sorrell held a lead of about 2 percentage points over challenger T.J. Donovan.
At about 11 p.m., with just over 40,600 votes cast, the difference between the two candidates was 614 votes.
Donovan told his supporters gathered at a Burlington hotel that they should go home.
Meanwhile, Windsor businessman John MacGovern handily defeated a Republican primary opponent in the race to challenge Vermont's independent U.S. Sen. Bernie Sanders in November.
Vermont election officials were predicting that about 8 to 10 percent of the state's registered voters would cast ballots in the primary.
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