Fergus County was created by act of the Fourteenth Legislative Assembly, Montana Territory, in the Spring of 1885. The Bill was sponsored by Hon. James Fergus, a delegate to the assembly from Meagher County, then including Central Montana.
The new county was to become operative through the selection of officers in November 1886, when the following were chosen: Sheriff, John Beck; Recorder, Win. H. Kelly; Clerk of District Court, Charles S. Fell; Probate Judge, Daniel A. Meagher; County Attorney, Frank E. Smith; Assessor, Michael Gurnett; Surveyor, L.W. Eldridge; Coroner, A.W. Sit ton; Superintendent of Schools, David Galbreath; County Commissioners, William Berkin, E.P. Chandler, J.P. Barnes.
The new county covered an area approximately 130 miles from east to west and 90 miles from north to south. It contained 209 townships, over 7,524 square miles and 4,824,000 acres..
The original Fergus County was subsequently divided into what are now entirely or partly the counties of Musselshell, Petroleum, Judith Basin, Wheatland, Golden Valley and the present Fergus County. The size of Fergus County at it's inception was greater than many of the New England States.