Bureau of Land Management
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The government has placed on line information regarding the issuance of public lands in those states where public lands were granted and/or sold. Start you land searching there if you are looking in the years of 1820-1908. They have images on line of the certificates. To obtain more information on your ancestor obtaining land, contact the National Archives Record Administration. Homestead and bounty land packets offer a great deal of information. See my NARA page for some of those.