The Big Sandy Expedition was an early campaign of the American Civil War in Kentucky that began in mid-September 1861 when Union Brig. Gen. William "Bull" Nelson received orders to organize a new brigade at Maysville, Kentucky and conduct an expedition into the Big Sandy Valley region of Eastern Kentucky and stop the build-up of Confederate forces under Col. John S. Williams. This was done in three phases. From September 21 to October 20, 1861, Nelson assembled a brigade of 5,500 Union volunteers from Ohio and Kentucky. On October 23, the southern prong secured Hazel Green and the northern prong West Liberty.