John S Johnston of Loudoun Co., Virginia and Shelby Co., Kentucky

I am looking for any information on John.  He married Sarah Gulick in Loudoun County, Virginia about 1796.  John moved to Shelby County, Kentucky with his seven children about 1815 after the death of wife Sarah.  Sarah Gulick's sister, Paatty Martha, also married a Johnston, Casper Johnston. I am assuming Casper and John are brothers but that is not proven. Ancestry.com has incorrect information, stating that John Johnston was born in Shippensburg, PA in April 1766.  It is the wrong John Johnston.