Sherrill defeated attorney and Assemblyman Jay Webber on Tuesday. Webber has held state office since 2008 and was backed by Trump on Twitter.
Sherrill is a former Navy pilot and prosecutor who has not held or sought office before and who built a massive campaign war chest.
The seat was up for grabs after 12-term Republican Rep. Rodney Frelinghuysen announced his retirement.
Mickey Sherrill addresses supporters
The district has been a GOP stronghold but just narrowly voted for Trump in 2016.
Sherrill campaigned on undoing the 2017 federal tax overhaul's cap on state and local tax deductions and stressed her support for health care for everyone.
Webber ran as a conservative backer of Trump.
Webber called his 11th Congressional District campaign "a dead heat, neck and neck, going down to the wire."
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The Democratic Congressional Campaign Committee (DCCC) targeted the district in its "red to blue" campaign, with Democrats hoping to flip 23 districts across the country from red to blue to re-take control of the House of Representatives.
The 11th, which includes parts of Essex, Morris, Passaic and Sussex counties, was an important part of that goal.
The district tilts slightly Republican, and even though Hillary Clinton won New Jersey in 2016, the 11th Congressional District went with Donald Trump, 49 to 48. The current congressman, Rodney Frelinghuysen, is a Republican who announced his retirement in January and who has held the seat since 1994.
"The mood in the district is angry and impassioned, and it's not positive," Fairleigh Dickinson University political scientist Peter Wooley said. "It's very negative emotion."
And Trump is a huge part of that divisiveness.
"I agree with the president when I think he's right, and I'll disagree with him when he's wrong," Webber said.
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Surprisingly, Sherrill said she was not harping on Trump, instead focusing on economic issues.
"People are really focused in this election cycle on how harmful legislation coming out of Congress has been for our state in particular," she said.
The Trump tax bill, approved earlier this year by Congress, could have a huge negative impact on taxpayers in New Jersey, as it reduces state and local tax deductions to just $10,000. Webber supports the bill, calling it a net gain in cutting overall taxes for New Jersey.
At a gas station in Denville, voters we talked with were split over Webber and Sherrill.
"This is a first for me," said Ken Hegarty, who voted for Trump in 2016 but says he may vote for Sherrill. "She impressed me."
Sherrill has run numerous TV commercials with her in front of a Navy helicopter pilot. In the ad, she says, "Before the Navy let me fly one of these I had to pass a lot of tests."
Hegarty's father flew a helicopter, which he says requires a lot of skill.
"It takes a lot of technique," he said. "Those commercials are getting to me."
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Another voter pumping gas, Chris Vernacchia, told us he was voting for Webber because he likes President Trump.
"I think Trump is a great guy," he said. "I think he's helping America a lot."
(The Associated Press contributed to this report.)
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