Grafton, WI, huh? Well, that's certainly a town steeped in blues history! Quite a few of the top bluesmen and women recorded there, as I'm sure you know. The best place to start is with a fellow who passed through there... Charley Patton. If there was a "Bible of Modern Music," the chapter on Patton might just as well be called Genesis.
Even though you said you're mostly interested in the modern stuff, it'd be good to get an idea of the music's early history... the history that Grafton was a part of. Charley Patton, Son House, Robert Johnson... those are the "Big 3" of Mississippi Delta Blues.
After that, the Blues heads north and finds a home in Chicago... Muddy Waters, Howlin' Wolf, Little Walter, Sonny Boy Williamson... the "Big 4" there. It's in Chicago where things start heading towards the more modern blues/rock style... this is the stuff that so much classic rock is based on... The Stones, Clapton, Led Zep...
Heading towards, and into, the modern: check out Magic Sam, Junior Wells, Albert King, Freddie King, Buddy Guy... Albert Collins... Bob Margolin... Robert Cray, Johnny Winter...
That should get you started, anyhow...
There are tons of artists, known and lesser-known, that are worth checking out and play a part in the history and progress of blues music.