"The suspect, a boyfriend of one of the female victims, drove to the residence, walked inside and began shooting people at the party before taking his own life," said a statement released by the Colorado Springs Police Department.
A motive has yet to be determined.
The massacre about 70 miles (110 km) south of Denver is the latest in a resurgence of mass shootings in the United States after such incidents seemed to recede during the height of coronavirus pandemic restrictions.
Among the incidents this year was one in Boulder, Colorado, where a man has been charged with 10 counts of murder for a shooting spree at a supermarket about 30 miles (50 km) northwest of Denver.
Colorado was also the state where two other deadly rampages took place, both in the Denver area: the 1999 shooting at Columbine High School that killed 15 people including the two perpetrators, and the 2012 shooting in a movie theater that killed 12 people and wounded about 70. The Aurora shooter is serving a life sentence.
Colorado Springs Police Chief Vince Niski said "my heart breaks for the families" in Sunday's attack and promised to support them.
"My vow to this community and to the families who have lost someone today, is that this department will do everything we can to find you the answers you deserve and be here for you with an unwavering support," Niski said in the police statement.
Police said they withheld releasing details of the shooting for several hours "in order to properly and respectfully notify family members of the deceased and ensure support was in place."The names of the victims will be released later, the statement said.