Johnston struggled to make a living for himself and his wife, who was ailing. He became president of a small railroad, the Alabama and Tennessee River Rail Road Company, which during his tenure of May 1866 to November 1867, was renamed the Selma, Rome and Dalton Railroad. Johnston was bored with the position and the company failed for lack of capital. He established in 1868 an insurance company in Savannah, Georgia, acting as an agent for the Liverpool and London and Globe Insurance Company, and within four years had a network of more than 120 agents across the deep South.