These abbreviations are used in 1830 census transcriptions that I have found in the library.
A Anderson B Bledsoe Bl Blount C Campbell Ca Carter Cl Claiborne Co Cocke F Fentress G Grainger Gr Greene H Hamilton Ha Hawkins J Jefferson K Knox M Marion Mc McMinn Mo Monroe Mr Morgan O Overton R Rhea Ro Roane S Sevier Su Sullivan W Washington