Democrats picked up full control of a half dozen statehouses Tuesday, while Republicans lost full control of four others.
The outcome could also affect the presidential election of 2020 and future control of the U.S. House of Representatives.
Most governors and many of the state legislators elected this year will be in office when congressional districts are redrawn after the 2020 Census. In some states, a governor's power to sign or veto congressional maps could decide the partisan balance.
State party control will also play an important role in the 2020 presidential campaign, especially in traditional battleground states like Florida, Ohio, Pennsylvania, Michigan and Wisconsin.
Congress now becomes split between Republican and Democratic control, and many keys issues like health-care reform may be decided in state capitols instead of Washington.
Democrats picked up full control of state government in Colorado, Illinois, Maine, New Mexico, New York and Nevada. Republicans lost full control to a divided government in Kansas, Michigan, New Hampshire and Wisconsin.
The shift in control came through a combination of changes in governorships and control of legislative chambers, many of which have been split between Republicans and Democrats.
After Tuesday's vote, Minnesota is now the only state where the legislature is divided — the Senate remains in Republican control, while the House flipped to Democrats. The last time there was only one divided state legislature was more than 100 years ago in 1914, according to the National Conference of State Legislatures.
Voters elected Democrats to succeed Republican governors in Illinois, Kansas, Maine, Michigan, Nevada, New Mexico and Wisconsin. Alaskan voters flipped the other way, electing a Republican governor to succeed a Democrat.
That gave Republicans in Alaska full control of state government, the only such gain for the GOP.
Democrats also kept control of Connecticut, a traditionally Democratic state that Republicans had hoped to pick up.
Despite their statehouse gains, Democrats lost high-profile governor's races in Florida and Ohio. A hotly contested governor's race in Georgia, where Democrat Stacey Abrams was seeking to become the first black woman to be elected governor of a U.S. state, remained too close to call on Wednesday.
In Florida, Democrat Andrew Gillum lost his attempt to become the state's first black governor, suffering a narrow defeat to Republican Ron DeSantis in a racially charged contest that drew national attention. Republicans also scored a major victory in Ohio's governor race, where Mike DeWine, the state attorney general, defeated Democrat Richard Cordray, who served as the first director of the U.S. Consumer Financial Protection Bureau.
But in Wisconsin, Democrat Tony Evers pulled off a narrow win in unseating Republican incumbent Scott Walker, according to NBC News. The two-term governor, who also survived a Democratic-driven recall election in 2012 after ending collective bargaining for public workers, briefly ran for president in 2016.
Democratic victories in governor's races in Michigan, Pennsylvania and Kansas — states that supported Trump in 2016 — bolstered the party's hopes of capturing those states in the 2020 presidential election.
In Michigan, Democrat Gretchen Whitmer turned back Republican Bill Schuette in the contest to succeed Republican Gov. Rick Snyder, who could not run again due to term limits. In Kansas, Democrat Laura Kelly defeated Kris Kobach, a staunch Trump ally, where former Republican Gov. Sam Brownback suffered from low approval ratings.