A house cat in rural Weld County tested positive for plague.
The Weld County Health Department says the cat got sick in early June. It is now getting treatment and is expected to recover.
Health officials say the plague could be passed on by fleas, other infected animals or rodents.
Prairie dogs were the first victims of plague in Colorado this year.
There were no human cases of plague last year or so far this year. Two people died of plague in 2015.