12th Regiment, Arkansas Infantry (Confederate)
12th Infantry Regiment was organized during the summer of 1861 by E. W. Gantt. Many of the men were recruited in Dallas County. The 12th had the unfortunate distinction of being captured in three engagements: Fort Donelson, Island No. 10, and Port Hudson. After being exchanged at Fort Donelson, the men were almost immediately exchanged and the regiment was reogranized. But after the fight at Island No. 10, many of its members refused to return to the comamnd and its ranks were filled with about 500 new recruits. Following the capitulation of Port Hudson, the men were exchanged, but the officers were sent to Johnson's Island. No attempt was made to reorganize the regiment. 
Companies in this Regiment with the Counties 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.
Many of the men were recruited in Dallas County.
See: EDWARD G. GERDES, Arkansas Civil War Regiments, Rosters and Muster Rolls, 
- Beginning United States Civil War Research gives steps for finding information about a Civil War soldier or sailor. It covers the major records that should be used. Additional records are described in 'Arkansas 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.
- Arkansas in the Civil War describes many Confederate and Union sources, specifically for Tennessee, 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.