You can but be prepared to keep them apart as adults. Chickens carry diseases that don't harm them but will kill peafowl. Peafowl can also kill chickens when they get aggressive during the breeding season.
@Midnightman14 is this true but only in close confines? I have chickens and peafowl that drink, eat, sit, even at times sleep in the same tree etc together for years. But they aren't caged and have a few acres to go as they please. I should add I've never once gave them anything in terms of medicine. Or is this only for chicks?
Free-range birds are generally healthier birds but are not immune to getting sick. You have been lucky so far but you should be prepared for any sickness that may pop up. You would be surprised how often they get sick on a weekend when you can't get to a vet or a store to get meds. My free-range birds don't get the worming treatments as regular as my penned bids and they rarely show any symptoms of being sick. We have chickens, guineas, swans, and ducks running free with about a dozen peafowl and they do fine. If you pen the peas and other birds then you should start a regular worming routine. Train your peas to take treats that you can soak with Safeguard for an easy way to deworm your peas while free to roam.