The 11 other victims were in stable condition, The (Colorado Springs) Gazette reported. It wasn't known if any were hit directly by the lightning.
The incident occurred 2-3 miles south of the Butts Army Airfield where the soldiers were taking part in training on a large, open field, Maj. Earl Brown, a 4th Infantry Division spokesman, told the newspaper. The soldiers were moving to shelter when the storm hit, the Army officer said.
"They were on their way to get to low ground, get into some vehicles and stuff, when they were struck by the lightning," Brown said.
"The cell basically built right over the top of Fort Carson."
It wasn't clear how much warning they had, he said.
"We have a big loud speaker and a siren goes off anytime there's a severe lightning warning in the area," he said.
Ten of the victims were taken to Evans Army Community Hospital and the other two to Memorial Central Hospital.
"Our hearts and prayers go out to the families when something like this happens, but Colorado is no stranger to lighting strikes," Brown said. "This is an unfortunate event."