Mountain Dog is right about Winfield...I used to live in Wichita...30 minutes away and I attended the first 12 festivals and 3 since...it has a WIDE variety of good music, and the best campground/parking lot picking to be found anywhere

Here in the Wash DC area there are several nice festivals each year, including a free festival each June(except this year!!*sniff*) at Glen Echo Park just north of DC....We have 400-500 performers in ethnic catagories you wouldn't believe-- as well as traditional American & British Isles...bookmark this page
WFF
and check it out....also there are other festivals including the Smithsonian Folk Festival, which is happening right now...Other DC area festivals