Chicago’s collar counties, which have slowly become more Democratic over several decades, lurched decisively to the left in Tuesday’s election in opposition to the politics of President Donald Trump and Gov. Bruce Rauner. 

The election of Democrats Lauren Underwood and Sean Casten to U.S. House seats once thought to be solidly Republican was only the most obvious evidence of the suburban shift.

There was plenty more, up and down the ballot.

The entire Democratic statewide ticket led by governor candidate J.B. Pritzker carried Lake, Kane, DuPage and Will counties, as well as suburban Cook, leaving the Chicago area without a reliably Republican bastion.

J.B. Pritzker and Juliana Stratton celebrate Tuesday night. | Ashlee Rezin/Sun-Times

J.B. Pritzker and Juliana Stratton celebrate Tuesday night. | Ashlee Rezin/Sun-Times

And in each of those counties, Democrats made important gains at the local level that could alter the political landscape for years to come.

OPINION

In Lake County, Democrats were celebrating their first majority on the county board in its 182-year history after picking up at least five seats Tuesday night, with two more still a possibility.

“I’ve been the chairman of the party for 27 years, and this was the best year we ever had,” said Sen. Terry Link of Vernon Hills, the Lake County Democratic chair.

Lake County Democrats also chalked up wins in the county clerk and treasurer races.

Link, who has been around long enough to see the pendulum swing both ways, wasn’t quite ready to mark Lake County in permanent blue marker on the political maps.

But, he added, “I can predict one thing: it will never be a red county again.”

The story was similar in Kane County, where Democrats flipped two county board seats, a judgeship and a state representative seat, while also taking back the sheriff’s office and carrying their portion of the Underwood and Casten congressional districts.

“I’d say we’re officially blue,” said Kane Democratic Chair Mark Guethle, who later backtracked slightly to say that the true test will be for Democrats to win a majority on the county board, now split at 12-12.

Still, Guethle called it the “best cycle ever” in his 16 years leading the Kane County Democrats.

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Illinois Democrats’ greatest success was probably in DuPage County, where the organizational efforts of the congressional candidates meshed with those of the Pritzker campaign, state legislative candidates and new grassroots groups to threaten what was once the Republican Party’s best stronghold.

DuPage Democrats won seven of 12 available seats on the 18-member county board after starting the day with just one. They also won the office of county clerk.

Two state Senate contests in DuPage County were still considered too close to call on Wednesday, but Democrats were optimistic about winning both. In the House, Democrats picked up one DuPage seat for sure with two others too close to call but looking good.

Will County Democratic candidates won all the countywide races on the ballot while also picking up county board seats. And in Cook County, Democrats eliminated two of the last four Republicans remaining on the board of commissioners.

Outside the Chicago area, however, the blue wave was more like an intermittent geyser that popped up in counties with university communities or a strong labor union presence. Altogether, Pritzker carried just 15 of Illinois’ 102 counties based on election night returns, although others were close.

Champaign County, home to the University of Illinois, saw Democrats sweep all five county offices, including two — sheriff and treasurer — where they hadn’t even fielded candidates four years ago.

“The party is as strong as it’s ever been,” said Doug House, president of the Illinois Democratic Chairmen’s Association.

Despite the big night, House, who hails from Rock Island County, couldn’t help but be disappointed that it was a rough night for his party in southern Illinois, where he believes three campaign appearances by Trump close to the election helped turn out a strong vote that saved GOP candidates.

“We’ve clearly got some work to do there,” House said of a region that was once as reliably Democratic as the suburbs were Republican.

In both places, Trump has hastened the trends.

“I would say Trump was probably one of our best organizers,” said Kane County’s Guethle, pausing before adding, “And Rauner.”