Perrin's Battalion, Mississippi State Cavalry
During the spring of 1864, the 11th Cavalry Regiment was formed using Perrin's Battalion State Cavalry as the nucleus. See 11th Regiment, Mississippi Cavalry for more details.
The 11th Mississippi Cavalry (Perrin’s), [formerly Perrin’s Battalion Cavalry (State Troops)], Internet site has a longer history taken from Dunbar Rowland's Military History of Mississippi, 1803-1898.
"Units of the Confederate States Army" by Joseph H. Crute, Jr. contains no history for this unit. 
Regiment Companies with the County of Origin
Men often enlisted in a company recruited in the counties where they lived though not always. After many battles, companies might be combined because so many men were killed or wounded. However if you are unsure which company your ancestor was in, try the company recruited in his county first.
Companies Comprising Perrin's Battalion:
Company B - (Choctaw Rangers) - raised in Choctaw County
Company E - (Rayburn’s Company) - raised in Newton County
Company G - (Thomas’ Company) - raised in Noxubee County, and Alabama
Company H - (Chickasaw Rangers) - raised in Chickasaw County
Company I - (Bookter’s Company) - raised in Oktibbeha County
- Beginning United States Civil War Research gives steps for finding information about a Civil War soldier. It covers the major records that should be used. Additional records are described in ‘Mississippi in the Civil War’ and ‘United States Civil War, 1861 to 1865’ (see below).
- National Park Service, The Civil War Soldiers and Sailors System, is searchable by soldier's name and state. It contains basic facts about soldiers on both sides of the Civil War, a list of regiments, descriptions of significant battles, sources of the information, and suggestions for where to find additional information.
- Mississippi in the Civil War describes many Confederate and Union sources, specifically for Mississippi, and how to find them.. These include compiled service records, pension records, rosters, cemetery records, Internet databases, published books, etc.
- United States Civil War, 1861 to 1865 describes and explains United States and Confederate States records, rather than state records, and how to find them. These include veterans’ censuses, compiled service records, pension records, rosters, cemetery records, Internet databases, published books, etc.
- Rowland, Dunbar, Military History of Mississippi, 1803-1898: taken from the Official and statistical register of the State of Mississippi, 1908 (Spartanburg, South Carolina: Reprint Company).
- Howell, H. Grady, For Dixie Land, I’ll Take My Stand!: A Muster Listing of All Known Mississippi Confederate Soldiers, Sailors, and Marines (Chickasaw Bayou Press, 1998).
- National Park Service, The Civil War Soldiers and Sailors System (accessed 11 January 2011)