Hi,
With respect to returning the box turtle to the wild, be sure to return it to the same area where you found it. Taking it miles away will only result in a treacherous return trip, as box turtles have strong homing instincts and do not leave the home range where they are born willingly.
Brently, if you found this turtle in your yard, your yard is likely part of it's home range, and you'll likely be seeing it again in the Spring.
If you would like to keep a box turtle, look into local turtle rescue groups. We have two native box turtle species here in NM and many turtles are turned in to a local rescue group by individuals unsuccessful with trying to keep them indoors. The group here regularly adopts out turtles to folks interested in setting up a proper habitat for needful turtles outside.
They do best outside as they can assume appropriate seasonal behavior--- hibernation, etc. It's difficult to set up the various microhabitats they require in captivity.
Here's a link to the group's site:
Turtle and Tortoise Care | Adopt a Turtle | Turtle Resources | Chelonians | Turtle Club Membership
They has some great care information. Also, with respect to feeding, don't use dog or cat food (often recommended for turtles). It can be deadly.
You're lucky to live in an area where turtles live naturally.