RDN - start with figuring out where they'd be. Are they in a prison or in county jail awaiting trial? If they've already been sentenced, are they doing minimum security time, medium, or maximum? I doubt they're doing maximum based on what you've said. From your post it sounds like they're probably in the county jail. We've got county inmates all over the place here, and they are out mowing the lawns, driving tractors, etc. That would be easy to walk away from. Get caught walking away and I think you move up to felony offense, which means you're not out mowing the lawn anymore.
To keep it simple, maybe look at your own state. Most corrections departments have some kind of web presence. They might even offer a tour. I've found most law enforcement types love to talk about their jobs, especially if you explain that you're a writer. There are also lots of forums online for questions about prisons, including forums for people with loved ones behind bars and forums for law enforcement types, most of which you can lurk in.
Once you've figured out the level of security you can start to figure out how to defeat it. I've done some writing about this, made most of it up as I went along, but used lots of web resources. I also stayed away from details. You can do a lot without using too much actual detail.
You might also try some googling about prison breaks. Good luck!
