It takes them a whole month to completely clear the prison, but once they do, they all get comfortable. There is the occasional walker at the gate, but they had found the keys and added metal plates to cover the gaps and make it safer. They raided all the local towns and houses and managed to make a large stockpile of food, baby stuff, and anything else they could ever need. Lori had her baby but ended up dying in the process. As the years go by, there seems to be fewer and fewer walkers, but the group stays right where they are, perfectly content with their place.