I know that Sebastion County is in Northwest Arkansas - I believe Fort Smith is the major city there. I've never researched there, but I do know that they've done a great deal to preserve all kinds of history...and the University of Arkansas is 45 minutes from there. They've got great research facilities at the U of A library in terms of old newspapers. Plus it's such a pretty area - definitely worth the visit if you ever get the chance. Clark County is in southwest Arkansas - Arkadelphia is the biggest city there. I've never done research there either...but have visited Arkadelphia many times. Columbia County is also in southern Arkansas. Little Rock is in Pulaski County - I live there. They have a place called the Arkansas History Commission, which is the history archives. I do most of my research there. They have an online website -
www.ark-ives.com I can't remember what all they have on the website, but I think they do have some stuff. And I don't know if they do research for people for a fee, but it might be worth checking out.