Where the suburbs moved left -- and how it swung elections

Democrats will have control of the U.S. House once again beginning in January, thanks, in large part, to their performance in America's suburbs.

Of the 41 congressional districts that Democrats turned from red to blue this election, 38 were in suburban districts, according to an analysis by The New York Times. (Democrats could pick up one to two more seats, once all votes are counted and elections are certified.)

But more granular than congressional districts overall are the counties that comprise them. For each suburban county, we mapped the percentage of ballots cast for the party that received the most votes in that county and looked at how that compared to 2016.

(Some counties span multiple congressional districts, and the maps do not break down the vote cast by county within each congressional district.)

The data came from The Associated Press vote tallies and the Centers for Disease Control and Prevention's designation of "suburban" districts.

Below are some of the suburbs that had the most dramatic turnarounds.

The South

Some of the biggest county flips in the South were in San Antonio, Austin and Houston in Texas, Memphis, Tenn., Charlotte, N.C., Oklahoma City and Atlanta. Democrats saw gains because of it between the metropolitan areas of these seven cities.

Atlanta

Two counties near Georgia's largest city flipped from red to blue this election: Cobb and Gwinnett counties. Cobb County, which spans three congressional districts, voted 54-46 for Democrats across those districts. It voted 61 percent Republican in 2016. Gwinnett, which also spans three congressional districts, voted 56-44 for Democrats.

Austin

Adjacent to Texas' most liberal major city, Democrats picked up majorities in two counties that voted for Republicans last election. Hays and Williamson counties voted by close margins for Democrats. Williamson County, which falls in Texas' 31st district, split 50-48 against Republican incumbent John Carter, who ended up winning the district by fewer than 10,000 votes.

Charlotte

Though no counties flipped from red to blue in the Charlotte area, Democrats made gains in several of them. In Union County, for example, the Democratic share of House votes went from 32 to 39 percent in the last two years. In nearby Cabarrus County, the share went from 38 to 44 percent.

Houston

Fort Bend County, southwest of Houston, changed from red to blue in the midterms. Sitting in the 9th and 22nd districts, Democrats went from getting 48 percent of the county's votes in 2016 to 54 percent this year.

Memphis

Just across Tennessee's state border with Mississippi, Marshall County voted 52-47 for the Democratic candidate challenging incumbent Republican Trent Kelly, who won re-election. Two years earlier, the county voted for Kelly 48-47.

San Antonio

South of the city, Atascosa and Wilson Counties flipped from red to blue. The counties voted overwhelmingly for Democratic incumbent Rep. Henry Cuellar over his libertarian opponent.

Oklahoma City

Each of the suburban counties surrounding Oklahoma City voted for Republicans, but the margins were tighter than they were in 2016. Democrats went from receiving 32 percent of House votes in Cleveland County to 41 percent, and from 20 to 24 percent in Lincoln County.

The West and the Midwest

Continuing a trend over the last few elections, Democrats won the West. President Trump, undoubtedly, was a major reason why. Trump's approval rating was just 37 percent in the West, in the latest NPR/PBS NewsHour/Marist poll. That was second only to the Northeast for lowest rating by region.

And Democrats saw big gains because of it — picking up several seats, particularly in California. Democrats also continued the trend of turning Colorado blue, fueled by the Denver suburbs.

The Midwest is turning into a true swing area. Trump was able to do well in places like Minnesota, for example. He only lost the state by less than 2 percentage points. But the Twin Cities metro area turned bluer than in 2016.

Chicago

In 2016, six of the seven suburban Illinois counties around Chicago voted Republican. This year, all of them voted for Democrats. One of the most dramatic turnarounds in the region was in McHenry County, where Democrats went from earning 40 percent of the House vote in 2016 to 51 percent this year. This helped propel Democrat Sean Casten, who knocked off Republican incumbent Peter Roskam.

Denver

Arapahoe County, just east of Denver, voted mostly in the state's 6th Congressional District, where Democrat Jason Crow unseated Republican incumbent Mike Coffman. The county, which voted mostly for Republicans in the last election, went for Crow by a 57-40 percent margin.

Nearby Douglas County, which favored Republicans, went from casting 30 percent of its votes for Democrats two years ago to 41 percent this year.

Los Angeles

Even though Orange County is just outside Los Angeles, the CDC's urban-rural scale technically doesn't consider it a suburb but a large central metro. Still, something big happened there that's worth noting. Orange County has traditionally had been an area dominated by Republicans, or at least a place where the GOP did well.

Consider that before these midterm elections, Republicans held four of the six congressional seats in Orange County. Come January, Democrats will control all six. What's more, every single congressional district that touches the Pacific Ocean was won by Democrats, except one in Washington State.

A note about California: San Bernardino County, which is geographically the largest suburban county in the United States and contains five different congressional districts, flipped from blue to red over the past two years. So what happened there?

California has a top-two primary system, where the two highest primary vote-getters advance to the general election regardless of party. In the 8th Congressional District, two Republicans advanced this year. This inflated the total number of Republican votes cast in the county. In 2016, the same thing happened in Orange County. There, two Democrats ran against each other in the state's 46th district.

Minneapolis-St. Paul

Washington County, east of St. Paul, cast 53 percent of its House votes for Democrats this year — up from 45 percent in 2016. The county is part of the state's 2nd Congressional District, where Democrat Angie Craig beat Republican incumbent Jason Lewis.

Portland

In the cross-state suburb, Washington's Clark County voted 51-49 against incumbent Republican Jaime Herrera Beutler. Yamhill County, southwest of Portland in Oregon, voted 50-45 in favor of Democratic incumbent Suzanne Bonamici. Both incumbents won their re-election bids.

The East

Nowhere is Trump's brand worse than in the Northeast, and within just four states — Virginia, Pennsylvania, New Jersey and New York — there were 11 Democratic pickups in districts that included suburban counties.

Like in California, these suburbs, full of well-off, educated people used to be prime GOP turf.

New York

Democrats made big progress west of The Big Apple in Morris County, N.J., where they went from receiving 37 percent of the vote in 2016 to 52 percent this year. This contributed to the defeat of incumbent Rep. Leonard Lance, as well as the Democrats flipping the state's 11th Congressional District from red to blue. That seat was previously a Republican stronghold and represented by retiring Rep. Rodney Frelinghuysen.

Pittsburgh

None of the suburban counties around the steel city flipped from red to blue, though they did move more in Democrats' direction. Beaver County, for example, went from voting 41 to 48 percent Democratic. And Fayette County went from 37 to 42 percent Democratic.

Philadelphia

Of the four suburban counties neighboring Philadelphia, only one — Delaware County — cast most of its House votes for Democrats in 2016. And even that was close; Delaware County voted just 52 percent for Democrats. This year, though, three went for Democrats.

And Delaware County? It went from being barely blue in 2016 to solidly Democratic this year at 62 percent.

Rochester, N.Y.

Democrats flipped two suburban counties surrounding the western New York city of Rochester: Niagara and Ontario counties. They also made a 15-point gain in Livingston County in the state's 27th congressional district, where Republican incumbent Chris Collins is under federal indictment for alleged insider trading.

Washington, D.C.

Democrats strengthened their lead in already-blue suburbs, and took back others around the nation's capital. In Frederick County, Md., for example, Democrats went from receiving 44 to 50 percent of the vote, and in Prince William County, Va., they went from 46 to a whopping 63 percent. Prince William contributed to Democrats' success in beating incumbent Republican Barbara Comstock.