10th Regiment, Mississippi Infantry
10th Infantry Regiment completed its organization in April, 1861, at Jackson, Mississippi. Its members were recruited in the counties of Adams, Claiborne, Lowndes, Itawamba, Warren, Marshall, Madison, and Yazoo. Few surrendered on April 26, 1865. The field officers were Colonels James Barr, Jr., Seaborne M. Phillips, Robert A. Smith, and James M. Walker; Lieutenant Colonels J.G. Bullard, Joseph R. Davis, and George B. Myers; and Majors James M. Dotson and Edward H. Gregory. 
10th Regiment Infantry article on Wikipedia gives a brief history of the unit, including places served, battles fought, and commanders.
The 10th Mississippi Infantry Web site has a longer history taken from Dunbar Rowland's Military History of Mississippi, 1803-1898.
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.
A Roster of the 10th Mississippi Infantry is arranged according to company.
"Old" [Original] 10th Mississippi
Company A - (Mississippi Rifles) - raised in Hinds County also listed as Co. D
Company B - (Ben Bullard Rifles) - raised in Itawamba County also listed as Co. A
Company C - (Port Gibson Riflemen, aka Port Gibson Rifles) - raised in Claiborne County also listed as Co. F
Company D - (Lowndes Southrons) - raised in Lowndes County also listed as Co. E
Company E - (Southern Avengers) - raised in Lowndes County
Company F - (Hill City Cadets) - raised in Warren County
Company G - (Rankin Rifles) - raised in Rankin County
Company H - (Bahala Rifles) - raised in Copiah County and Marshall County
Company I - (Madison Rifles) - raised in Madison County
Company K - (Yazoo Minute Rifles) - raised in Yazoo County
The term of enlistment expired in March, and the regiment was reorganized at Corinth on March 15, 1862 for a term of two years.
"New" 10th Mississippi
Company A - (Horn Lake Volunteers [formerly Co. E, 9th MS Infantry]) - raised in DeSoto County
Company B - (Natchez Southrons [also listed as Co. C]) - raised in Adams County
Company C - (Ben Bullard Rifles [also listed as Co. D]) - raised in Itawamba County
Company D - (Mississippi Rifles [also listed as Co. G]) - raised in Hinds County
Company E - (Lowndes Southrons) - raised in Lowndes County
Company F - (Port Gibson Rifleman) - raised in Claiborne County
Company G - (Fulton Guards [also listed as Co. B]) - raised in Itawamba County
Company H - (Rankin Rifles [also listed as Co. A]) - raised in Rankin County
Information from Military Annals of Mississippi: Military Organizations which Entered the service of the Confederate States of America from the State of Mississippi, by John C. Rietti, Spartanburg, south Carolina: Reprint Company Publishers, 1976, p.86. FHL book 976.2 M2r
Company I - (Bahala Rifles) - raised iln Copiah County
Company K - (Beauregard Relief) - raised in Tippah County
Company L - (Capt. Finley’s Company)
Company M - (Capt. Dobson’s Company)
Company N - (Capt. Bell’s Company)
Company O - (Capt. Inge’s Company)
Company P - (Capt. Betts’ Company)
- 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.
- 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), FHL book 976.2 M2
- 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), FHL book 976.2 H2
- Rietti, John C, 1841-1896. History of the organization, military service, and a record of, battles and marches, of the Mississippi Rifles, Companies A and D : Tenth Regiment Mississippi Volunteers, General J.R. Chalmer's High Pressure Mississippi Brigade, Confederate States Army, from the organization of the Company at Jackson, Miss., January 1858, to the surrender of General Johnston's Army, April 26, 1865. (Bethesda, Maryland: University Publications of America, c1990), FHL fiche 6082497
- National Park Service, The Civil War Soldiers and Sailors System (accessed 11 January 2011)