Republicans will hold the Senate majority for at least two more years.
The GOP held a 54-seat majority in the Senate entering the elections with most pundits figuring Democrats would pick up at least a few seats.
While Democrats picked up one seat early in the night with a win in Illinois, Republicans held off challenges in several contested states.
The contest in New Hampshire has not been called, while the Louisiana Senate race will have a runoff in December. Democratic Gov. Maggie Hassan declared victory in New Hampshire, but incumbent Republican Sen. Kelly Ayotte is not conceding.
Unofficial results have Hassan up by fewer than 700 votes, according to AP but the race is too close for AP to call.
But the GOP retained control of seats in Pennsylvania, Missouri, Wisconsin, Indiana, Ohio, North Carolina and Florida to keep the Senate. The GOP also will control the House of Representatives, according to the Associated Press.
GOP Incumbent Roy Blunt beat Missouri Democrat Jason Kander, Sen. Pat Toomey (R-Penn.) defeated Democrat Katie McGinty to retain the Senate seat in Pennsylvania and Sen. Ron Johnson (R-Wisc.) fended off Democrat Russ Feingold in a rematch of Wisconsin's 2010 Senate race to keep the seat.
Elsewhere, Sen. Richard Burr (R-North Carolina) won his re-election campaign in what was considered one of the tightest Senate races in the country.
Democrats hold 47 seats and Republicans hold 51 seats with two seats remaining. Democrats have been counting on picking up seats held by Republicans in Illinois. The best chance for Republicans to pick up a seat was Nevada where Senate Minority Leader Harry Reid is retiring, but Democrat Catherine Cortez Masto beat Republican Joe Heck, according to AP.
Democrats picked up a seat early in the night when Tammy Duckworth beat Sen. Mark Kirk (R-Ill.) for the Illinois Senate seat. The seat was widely considered to be the seat most likely for Democrats to pick up.
Democrats, however, missed two potential opportunities to pick up Senate seats in Florida, Ohio, Wisconsin, Pennsylvania, Missouri, Indiana and North Carolina.
Sen. Marco Rubio, a 2016 presidential candidate, has won re-election for his seat in Florida, AP reported. Rubio faced Rep. Patrick Murphy. Rubio originally intended to not run for re-election while running for president but opted to seek re-election after his presidential hopes faded.
Ohio Republican Sen. Rob Portman has won re-election, according to AP. The Ohio seat originally was expected to be close, but Portman has had a large, steady lead against former Ohio Gov. Ted Strickland.
Of the Senate races expected to be the closest, Burr topped challenger Deborah Ross in North Carolina in one of the tightest races in the country.
In Indiana, Republican Congressman Todd Young won a tight race against former Democratic governor and senator Evan Bayh. Young will replace Republican Sen. Dan Coats, who is retiring.
As predicted, AP has called the Senate races in Vermont for Patrick Leahy while GOP senators Tim Scott and Rand Paul both won easily.
Incumbents Richard Blumenthal (D-Conn.) and James Lankford (R-Okla.) both won their respective elections, according to AP. Chris Van Hollen won the race for Maryland's open Senate seat. Sen. Richard Shelby (R-Ala.) was re-elected in Alabama.
In later results, Sen. John Hoeven (R-N.D.), Sen. John Thune (R-S.D.) and Sen. Jerry Moran (R-Kan.) all retained their seats for the GOP, while Sen. Charles Schumer (D-NY) held his spot for the Democrats.
Sen. John Boozman has won his race to retain his seat in Arkansas and Sen. Johnny Isakson retained his seat in Georgia, according to AP.
Incumbents Sen. Chuck Grassley (R-Iowa) and Sen. Mike Lee (R-Utah) both won their respective elections.
In later results, Sen. John McCain (R-Ariz.) won his re-election campaign against Rep. Ann Kirkpatrick, while Sen. Michael Bennet (D-Colo.) also won his re-election campaign.
Sen. Patty Murray (D-Wash.), Sen. Brian Schatz (D-Hawaii) and Sen. Mike Crapo (R-Idaho) all won their re-election bids.
Kamela Harris, meanwhile, took the Senate seat in California vacated by Barbara Boxer, who is retiring.
Republican State Treasurer John Kennedy advanced to a December runoff for the Louisiana Senate seat that will be vacated by Republican David Vitter. Kennedy will face Democrat Foster Campbell.
Incumbent Ron Wyden (D-Ore.) won his re-election campaign, while incumbent Lisa Murkowski (R-Alaska) also retained her seat, according to AP.