Box turtles can live just about anywhere in the lower 48 states if your build them a good pen. A pen should have lots of shade for those hot summer months, and the soil should be deep enough that they can burrow into the ground (sometimes up to 2') to escape the winter's cold). I have 11 boxies that live outdoors year round. In the winter they burrow underground and when the weather is right they come back to the surface to live for the duration of summer.
The best place to aquire a box turtle is by adopting one through turtlehomes.org or coloradoreptilerescue.org or any other adoption facility. By adopting a box turtle that needs a home your not helping in the destroying of there wild numbers which are in a terrible decline due to cars, and the pet trade.
You can adopt a box turtle no matter what its age is.
Before building a pen you need to think a few things through. Do you have preditors such as dogs, coons, oppossoms, or cats that could injure a turtle. If so you will probley need to place a net or something over the pen to keep them out. How many turtles do you want? The more turtles you have the bigger the pen should be, specially if your going to house multiple males together. Also remember turtles can escape anything if not built turtle proof. Make sure the walls to your pen go underground at least 1', and I would go even deeper then that.