The Sherman County Clerk, www.sherman.county.com/govt__clerk.asp has marriage records from May 1889 to the present. You'll need a copy of their marriage license to find out Mr. jackson's first name. Then you can work on where and when he was born and where and when he died.
Generally divorce records are held at the county court. Maybe the County Clerk can provide more info about where you can find them. Successful Searching!