Harris County Democrats rode a surge in voter turnout to a decisive victory on Tuesday, unseating several countywide Republican officials, including longtime County Judge Ed Emmett, and sweeping all 59 judicial races.

Emmett, who courted Democratic ticket-splitters and leaned on his reputation as a steady hand during hurricanes, conceded at 11 p.m. to 27-year-old challenger Lina Hidalgo, who was running in her first race for public office.

After defeating the Republican sheriff and district attorney two years ago, Harris County Democrats now will control all of the countywide elected posts. In addition, former sheriff Adrian Garcia defeated incumbent Republican Jack Morman in the Precinct 2 commissioner’s race, giving Democrats control of Commissioners Court.

“This year with the turnout we saw, we all stepped up. We realized that democracy depends on participation and we stepped up,” Hidalgo said to more than 100 supporters at the Harris County Democrats watch party.

The crowd chanted her name before she took the stage.

Hidalgo, a Colombian immigrant and Stanford University graduate who returned to Houston last summer to launch her campaign, now finds herself the incoming executive of the third-largest county in the U.S.

University of Houston political science professor Brandon Rottinghaus attributed the Democrats’ success to changing demographics in the largest Texas county and a superb get-out-the-vote effort by Democratic groups.

“Democrats have harnessed the blue wave, at least locally,” Rottinghaus said. “Harris County is going to be trending more purple, which is going to spell difficulty for Republicans in countywide races in the future.”

The upset fulfilled the nightmare scenario Republicans feared: Democratic straight-ticket voters who have a positive opinion of Emmett failed to venture far enough down the ballot to vote for him, handing the win to Hidalgo.

Hidalgo will be the first Latina county judge, and youngest since a 23-year-old Roy Hofheinz was elected in 1936. She has lived in Harris County sporadically as an adult and has never attended a meeting of Commissioners Court.

Hidalgo was an energetic campaigner who implored voters not to settle for the status quo. She criticized Emmett for failing to push harder for flood protection measures in the decade before Hurricane Harvey, when parts of the county were flooded by several storms. Emmett had campaigned on his record, contrasting his 11 years as the county’s chief executive with Hidalgo’s lack of formal work experience.

At Emmett’s watch party at the Hotel ZaZa, his supporters stared in disbelief at monitors displaying the results. Emmett spoke briefly and compared this election to the 1974 midterms following the Watergate scandal, when a wave of incumbents were defeated.

"If this happens the way it appears, I won't take it personally," Emmett said. "It is a bitter pill to swallow, but Harris County will move on. I will be fine."

Supporter Xavier Stokes chalked up the county judge race result to straight-ticket voting, rather than a referendum on Emmett himself.

“He’s done such a good job, and yet here we are,” Stokes said. “It just shows you how this type of voting distorts the outcome.”

The lone bright spot for local Republicans was the Precinct 4 commissioner’s race, where incumbent Republican Jack Cagle cruised to victory over Democrat Penny Shaw.

In the Precinct 2 race, Morman heavily outspent Garcia and tried to cast the former Harris County sheriff as a political opportunist seeking a rebound after failed bids for mayor of Houston and the House of Representatives.

Garcia, a gregarious campaigner who could detain a stranger for an hour in conversation regardless of his wishes, emphasized shoe-leather politicking. He recruited a campaign staff to canvas throughout the largely Hispanic precinct to engage constituents from whom he said Morman too seldom sought input. Morman’s flood-the-airwaves strategy included ads attacking Garcia.

Emmett focused his ad buys on convincing Democrats to vote for him, as much a hedge against a predicted blue wave as a natural strategy, given his broad popularity. The other countywide Republicans targeted only their base voters, at their peril. Democrats dispatched them, one after the other: Diane Trautman defeated County Clerk Stan Stanart, Marilyn Burgess beat District Clerk Chris Daniel and Dylan Osborne edged County Treasurer Orlando Sanchez.

The judicial races likewise were a Democratic rout. The party won each of 23 seats on the district judge bench, all 13 on the family court, all four for county civil judge, all 15 county misdemeanor judges and all four county probate judges.

The sweep of the misdemeanor bench, which was dominated by Republicans, could have huge ramifications for the future of the federal lawsuit, brought by poor defendants, challenging Harris County’s cash bail system. Each of the 16 jurists are defendants, including some who have pushed the county to continue fighting the case, though it already has cost taxpayers more than $6 million.

Emmett’s surpise defeat likely ends his political career, which began in his twenties when he was elected to the Texas legislature. Emmett was widely praised for his leadership during storms, and his tenure as county judge was bookended by Hurricane Ike in 2008 and Harvey this past year.

Emmett, 69, suffered a minor stroke last summer but said he was in good health and eager to serve at least another term. He was instrumental earlier this year in building public support for the county’s $2.5 billion flood bond, which voters approved with 86 percent support in August.

Staff writers Sarah Mikati, Ileana Najarro and Shelby Webb contributed reporting.

Zach Despart covers Harris County for the Chronicle. You can follow him on Twitter or email him at zach.despart@chron.com.