Bounty Land Grants 

According to some things I have read (including "U.S. Military Records:  A Guide to Federal & State Sources" by James C. Neagles):

Beginning about the time of Revolutionary War, bounty-land grants were used by the government to entice men to join the military.  Free land in the public domain was given to men in return for military service.  This practice continued until 1855.  They were replaced in 1862 with the Homestead Act.

A soldier had to fill out an application ( whether he was approved and given the grant or not, this application would be a valuable source) and when approved a "warrant" was issued for a specified number of acres.  The claimant located a desired piece of land in the public domain and then turned in his "warrant" for a "patent" which gave him title to the land.

Revolutionary War grants were for land in the Military District of Ohio.  For the War of 1812, land in the territories of Arkansas, Illinois and Missouri.  This is very important, because Iowa was part of Missouri from 1812 to 1821.  Grants issued after 1842 (but not for Rev. War service) were for land in the public domain.  

Except for grants issued for service in the War of 1812, soldiers could, and quite often did, sell their grants.  If a soldier's grant was for land in the Military District of Ohio and he didn't want land there, he could apply for an Exchange Certificate for public land.

The National Archives has an alphabetical list of warrants issued but the info has been incorporated into the soldier's pension file.

National Archives microfilm rolls M804, M805 and M829 concern Revolutionary War Pension & Bounty-Land Warrant Application Files 1800-1900.  M848 concerns 1812 Military Bounty-Land Warrants 1815-1858. Most libraries can order these films for you.   There are also several published sources regarding pensioners & bounty-land recipients.  

The Missouri State Historical Society and the Missouri State Archives both have information on bounty-land warrants.  You can get there through the USGenWeb site.  I know the Archives accepts look-up requests via email.

Land Records

Iowa is a federal-land state. Lands were generally acquired from the government or other individuals. Patents, tract books, and township plats for government transactions are available at the Bureau of Land Management Eastern States Office in Springfield, Virginia. Holdings for Iowa land records at the National Archives/Central Plains Region include abstracts of military warrants. More federal military bounty land warrants were used in Iowa than any other state. Records of homesteads, including certificates, receipts, and entries, are held for Des Moines, Fort Dodge, and Sioux City. Many are also found at the National Archives in Washington, D.C.. The "Auditor of State Abstracts of Original Land Entries," 1847—59, has been microfilmed and is available to researchers.

Following the federal disbursement of land in Iowa, land purchases and sales were handled by the individual county recorder, beginning with the establishment of that particular county. The cooperative microfilming project of the Genealogical Society of Utah and the State Historical Society of Iowa have provided the preservation of land conveyances for almost every county. For further information, consult: 

Lokken, Roscoe L. Iowa Public Land Disposal. Iowa City: State Historical Society of Iowa, 1942.

Hone, E. Wade. Land and Property Research in the United States. Salt Lake City: Ancestry, Inc., 1997.

Bureau of Land Management

The Bureau of Land Management has made some major improvements on the General Land Office, Land Patent Records site at: https://www.nifc.gov