Many military records are found at the Family History Library, the National Archives, and other federal and state archives. The U.S. Military Records Research Outline(34118) provides more information on the federal military records and search strategies. For Arkansas the following sources are also very helpful:
Forts
Little Rock Barracks -- Textual records of this post, 1864-1890, including registers, reports, and correspondence, are in the National Archives and are described in Records of United States Army, Continental Commands, 1821-1920, under the section entitled Records of Posts, 1820-1940 (Record Group 393.7).
Post of Washington -- Textual records of this post, 1867-1869, including registers, reports, and correspondence, are in the National Archives and are described in Records of United States Army, Continental Commands, 1821-1920, under the section entitled Records of Posts, 1820-1940 (Record Group 393.7).
War of 1812 (1812-1815)
Bounty land in Arkansas, Illinois, and Missouri was granted to soldiers who served in the War of 1812. Copies of the bounty land warrants are available at the Family History Library (FHL films 983163-77 index on 983163). They provide the name of the soldier, rank, unit, and date of warrant. A list of 6,600 grantees, arranged by county name, is in Katheren Christensen, comp., Arkansas Military Bounty Grants (War of 1812)(Arkansas Ancestors, 1971; FHL book 976.7 R2c).
Civil War (1861-1865)
Soldiers from Arkansas served in both the Union and Confederate armies. Indexes and the compiled military service records are available at the Family History Library and the National Archives.
Arkansas pension records for Confederate veterans are located at the Arkansas History Commission. A searchable index to Confederate pension records is posted by the Arkansas History Commission. The Family History Library holds microfilm copies of Arkansas Confederate pension records, 1901-1929, on 121 films. The pensions are alphabetically arranged. (FHL Films beginning with 1722443) Copies of individual pension records may be ordered from the Arkansas History Commission. Pension records for Union veterans are available only at the National Archives. The Family History Library has an index of Union pensioners.
In 1911 a special census was taken of Confederate veterans. Returns are available for 40 of the 75 counties. Abstracts of the questionnaires have been published in Bobbie J. McLane and Capitola H. Gazner,Arkansas 1911 Census of Confederate Veterans, Three Volumes. (N.p.: Arkansas Ancestors, 1977-1981; FHL 976.7 X2m; fiche 6019335). An index has been published by the same authors (FHL 976.7x2m index). All of these censuses are at the Arkansas Historical Commission, and most are on microfilm at the Family History Library.
World War I (1917-1918)
World War I draft registration cards for men age 18 to 45 may list address, birth date, birthplace, race, nationality, citizenship, and next of kin. Not all registrants served in the war. For registration cards for Arkansas, see:
United States. Selective Service System. Arkansas, World War I Selective Service System Draft Registration Cards, 1917-1918. National Archives Microfilm Publications, M1509. Washington, DC: National Archives, 1987-1988. (On FHL films beginning with 1522740.)
To find an individual's draft card, it helps to know his name and residence at the time of registration. The cards are arranged alphabetically by county, within the county by draft board, and then alphabetically by surname within each draft board.
Most counties had only one board; large cities had several. A map showing the boundaries of individual draft boards is available for most large cities. Finding an ancestor's street address in a city directory will help you in using the draft board map. There is an alphabetical list of cities that are on the map. For a copy of this map see:
United States. Selective Service System. List of World War One Draft Board Maps.Washington, DC: National Archives. (FHL film 1498803.)
Online Resources
The WWI draft cards are digitized, indexed and online at www.ancestry.com ($)
http://www.couchgenweb.com/civilwar/
http://www.geocities.com/Area51/Lair/3680/cw/cw-ar.html
http://www.accessgenealogy.com/military/civil/rosters/arkansas.htm
http://www.rootsweb.com/~usgenweb/pensions/civilwar/arindex.htm
http://www.civilwarbuff.org/links.html
http://www.arkmilitaryheritage.com/exhibits/wwi.htm
http://www.archives.gov/research/arc/ww2/army-casualties/arkansas.html