Boulder Police said the child was located safely, seized from the custody of her biological father Adam Densmore, 32.
Police said they picked up Densmore in Oklahoma just outside of Tulsa, but the baby's mother was not with Densmore.
Mead has family in Pennsylvania and Louisiana and has lived in the Boulder area for at least five years, Boulder Police said. Densmore has lived in the area off and on for some time.
"They had a very strained relationship," said Shannon Cordingly, with the Boulder Police Department. "At this point, we are treating this investigation very seriously. She hasn't been heard from since 5:30 Sunday."
Mead's neighbors describe a quiet couple, who had a small argument last week.
"It sounded like they were just kind of arguing Thursday, but it wasn’t like anything you would hear like a domestic disturbance or anything," said Lucas Swafford, who frequently stays in a nearby apartment. "My kids were playing with their little girl the other day. It's just sad."
Friends describe Mead as a pre-school teacher working on an internship to develop career skills.
"She's incredibly intelligent, a sweetheart, classy, just seemed like a really good mom," said Christina Ball, who is in the internship with Mead and lives next door.
Ball said it was strange last week when she saw Winter wandering in the apartment complex.
"I’m standing there watching her making sure she’s okay, and she’s not going to hurt herself or anything like that, and it was, like, 15 minutes later and he finally comes out. I thought that was kind of odd," said Ball.
Police say an Amber Alert in Colorado was not issued because the case did not meet the criteria.
Anyone with information is asked to call the Boulder Police Department at 303-441-3333.