Three other children and a woman who ran the day-care escaped unharmed, Aurora fire Capt. Chris Henderson said.
Deputy George Gatchis, who works for the sheriff's department in neighboring Denver, was driving home from work when he saw smoke.
After the woman told him a baby was still inside, Gatchis crawled on his belly through the dark, smoke-filled house calling out for the 3-month-old boy, who was in a car seat in the living room, Aurora police Detective Larry Martinez said.
Twice he tried to reach the boy but had to turn back, and he nearly lost consciousness on the second attempt, Martinez said. Gatchis was treated for smoke inhalation and released.
``He's obviously very, very upset he couldn't get to the baby,'' Martinez said. ``This man is truly a hero.''
An Aurora firefighter was also treated and released, but the nature of his injuries was not available.
Fire trucks arrived at the house seven minutes after the blaze was reported, but the baby was dead by the time rescuers reached him, Henderson said.
No other names or ages were immediately released. The woman who escaped the fire was the parent of at least one of the surviving children, but the child who died was not her own, Henderson said.
The fire's cause was under investigation.
No state day-care license had been issued for the house, but it was not clear whether one was required, said Department of Human Services spokeswoman Liz McDonough. A state license is required for any family day-care with children from more than one outside family, she said.
McDonough said the department had received no complaints about the home.
