The Louisiana Purchase in 1803 brought (what is now) Arkansas into the United States. The area was thrown open for settlement at that time.
The area was part of the Missouri Territory in 1812, and became Arkansas Territory in 1819 when Missouri applied for statehood. The area encompassed what is now Oklahoma. On June 15, 1836, Arkansas became the twenty-fifth state in the union.
Some very early records, 1803-1836, may be found in Louisiana, Missouri and Oklahoma collections.
The Bureau of Vital Statistics, State Health Department, State Health Bldg., Little Rock, Arkansas, has birth and death records from 1914, and marriage records from 1917. Some City Clerks might have birth and death records before 1914. Clerks of counties where license was obtained also have marriage records. County Clerks, or Clerks of Circuit Courts also have records of wills, deeds, divorces, and war service. Naturalization records are filed with Disrtrict Courts in Little Rock, Helena, Batesville, Fort Smith, and Texarkana.
Federal census are available since 1830.
US Government surveys, original field notes, books showing original entries by Township and Range, are available at the State Land Office, State Capitol Bldg., Little Rock.
Southwest Arkansas Regional Archives, in the 1874 Courthouse, Old Washington State Park, (P.O. Box 98, Washington, AR 71862), near Hope, has become one of the most valuable sources for the Arkansas researcher. They will do simple mail-in lookups free and more extensive ones for $5 an hour BUT more importantly, they are not state funded and need donations to keep records and equipment, etc. going. The workers are all volunteers and the state provides only the building and utilities. This is such an important facility that we should all use it - wisely. Visitors will be impressed by the knowledge about the region that the librarian has and her helpfulness. So much of what is available online is not documented, so this kind of facility is even more important to a thorough researcher. Don't forget the SASE if you write!!
The Grace Keith Genealogical Collection of the Fayetteville, AR, Public Library, 217 East Dickson St., Fayetteville, AR 72701 also holds valuable information. The facility is on Hwy 71B east of the courthouse and the University of Arkansas at Fayetteville. The collection focuses on Northwest Arkansas, although there is information about every state. Virginia, North Carolina, South Carolina, Georgia, Kentucky, Tennessee, Pennsylvania, Missouri, and Maryland are particularly well represented.
This is not a complete listing of sources, but is offered to help you find your way into some of the materials available.
You might also wish to visit the State page at Arkansas or the Arkansas Historical Commission which contains, in their "material" link, a number of historical articles.