Democrats gain three seats to win a 19-16 majority.

When the Colorado General Assembly is gaveled into session in January, Democrats will be the majority party in the state Senate. Republicans entered Election Day holding a slim 18-16-1 majority, but Democrats won three seats to take control of the chamber.

Democrats last controlled the state Senate from 2012 to 2014, before ceding its leadership to Republicans.

With Democrats gaining the state Senate and holding onto the state House of Representatives, the party now controls a trifecta on Capitol Hill after Democrat Jared Polis was elected governor.

Seventeen of the state Senate’s 35 seats were up for election. Six seats were considered battleground districts, and Democrats held ground in the three that they already had, and they picked up three seats from two Republicans and an independent.

Tammy Story, Faith Winter and Jessie Danielson won the seat in State Senate Districts 16, 24 and 20, respectively.

Democratic victories on Capitol Hill and the Governor’s Mansion reflect the party’s domination in key statewide races. Polis defeated Republican Walker Stapleton in the governor’s race. Democrat Jason Crow defeated five-term incumbent Rep. Mike Coffman in Colorado 6th Congressional District. Crow’s victory helped Democrats take control of the U.S. House of Representatives.

Democrat Jena Griswold won election to Colorado secretary of state, and Democrat Dave Young won state treasurer.

State Sen. Leroy Garcia (D-Pueblo) told 9NEWS he plans to run for Senate president. The senate Democratic Caucus will elect the senate president and majority leader in the coming days.