The temporary shelter Downtown on Smithfield Street closed at 7 a.m. Wednesday.
It was supposed to close in March, but Allegheny County kept it open due to increasing homelessness.
The decision to close the shelter was driven by a lack of air conditioning and complaints from businesses and residents.
The county found spots for the core group staying at the shelter, saying 20 other facilities are better suited to meet their needs.
The director of the county's Department of Human Services says they've offered places to stay to as many as 125 people but not everybody accepts.
Some homeless advocates are calling the decision to close the shelter cruel.