Durango attorney Ellen Roberts beat Democrat Bruce Whitehead to take the 6th Senate District in Tuesdays general election.
With almost all votes counted, Roberts defeated Whitehead 32,484 votes to 21,474.
She won La Plata County 11,200 to 8,520, or 57 percent to 43 percent, with all votes counted.
A Republican hasnt held the seat since 1999.
Roberts will be the first woman to hold the seat.
She said Tuesday night she was waiting for more certainty before claiming victory.
Whitehead took only two counties in the eight-county district: San Juan and San Miguel.
Roberts has represented the 59th District in the Colorado House of Representatives since 2006. Tuesday, fellow Republican J. Paul Brown beat Democrat Brian ODonnell to take over her seat in the House.
The race between Whitehead and Roberts was hard-fought, but not as close in the end as her bout with primary challenger Dean Boehler, a Norwood businessman with tea party sympathies. She beat Boehler 53 percent to 46 percent in August.
She went on to raise $140,150 in campaign donations, to Whiteheads $122,428.
Whitehead was unopposed in his primary, having agreed with the Democratic selection committee members to run to retain the seat when the term was up.
He could not be reached for comment Tuesday night.
Whitehead is a former division engineer for the Colorado Division of Water Resources.
He was appointed to replace fellow Hesperus Democrat Jim Isgar in August 2009, when Isgar was appointed by the governor to head a the Colorado USDA office in Denver.
Isgar was elected to the seat in 2001.
Democrat Jim Dyer served in the seat from 1999 to 2001.
Republican Ben Alexander of Montrose served from 1995 to 1999.
Before him, Democrat Sam Cassidy of Pagosa Springs served from 1991 to 1995, and Republican Bob DeNier of Durango served from 1987 to 1991.
Colorado state senators serve four-year terms; House representatives serve two-year terms. Term limit restrictions limit senators and representatives to eight years in each body.
The state is divided into 35 Senate districts with approximately 123,000 citizens each and 65 representative districts with approximately 65,000 citizens each.
The 6th District is made up of eight counties: La Plata, Montezuma, Archuleta, San Juan, Dolores, Ouray, Montrose and San Miguel.
The 59th features four counties: La Plata, Montezuma, part of Archuleta and San Juan. The largest city in both districts is Durango.