Dobbs County (now abolished) was form in 1758 from Johnston County. See also, Johnston, Craven, Pitt, Jones, Glasgow, and Lenoir counties when researching your ancestors.
This county has seen many border changes over the years that researchers should be aware. See The Formation of the North Carolina Counties, 1663-1943, by David Leroy Corbitt for a complete history of the county formation. (Affiliate Link)