State armies are interesting organizations (I am endlessly fascinated with the Missouri State Guard). A while back when I was casually researching northern militia units I came across an organization called the Indiana Legion. Unfortunately, I didn't have the time to find much data or background about it beyond some uniform information for the various units. Now I see a fellow named John Etter has written a book-length monograph The Indiana Legion: A Civil War Militia (no publisher information that I could find).
Along similar lines, I've been meaning to check out William Harris Bragg's works Joe Brown's Army: The Georgia State Line, 1862-1865 and (with William Scaife) Joe Brown's Pets: The Georgia Militia, 1862-1865. If you've read either of them, feel free to comment below!