Here is some information that I've found on the Mississippi State Troops:

STATE TROOPS. MAINLY TROOPS OF 1864.

In August, 1864, Governor Clark was authorized to call out every able-bodied man in the State to repel invasion, and all capable of bearing arms were called to assemble at Grenada, Okolona or Macon. In August also, the Legislature authorized General Forrest to order on military duty for thirty days boys and men between the ages of 16 and 55 years.

Col. J. J. Pettus, commissioned August 8, 1864, was put in command of rendezvous at Grenada, with P. S. Layton as his Adjutant. Col. John M. Simonton, commissioned August 13, was assigned to command of the rendezvous at Okolona. Col. Jeptha V. Harris, commissioned August 26, was in command at Macon. There was also a rendezvous at Brandon, under Colonel Thornton. Col. O. J. E. Stewart commanded District No. 5.

So, the State Troops were basically an short-term emergency enlistment of any man left that could shoot a gun. I found this information here:

http://mississippiscv.org/MS_Units/MS_ST_Troops_Inf.htm

Alfred Sartin was my great-great grandfather. By the way, Major, William, John, and Leader were his brothers. He had two sons in the war, James and Samuel.