According to statistics 2.3 Million people are incarcerated in the United States! 2.3 Million- and that was as of 2007.
If you've known anyone in prison, and I have, their lives are generally very hopeless and bleak. Without negating there circumstances that brought them to these place, these are folks who still need love and encouragement.
Prison Fellowship Ministries is a great place through which to serve should you feel drawn. Check them out here.