National Personnel Records Center (NPRC) in St. Louis.
NPRC holds Official Military Personnel Files (OMPF) and other personnel-related records for both the military and civil services of the United States Government. Records are classified as archival 62 years after the service member's separation from the military.
Try to find the most information you can before contacting NPRC.
There were no pensions granted to WWI veterans from the federal government. In 1924, a law was passed to award them bonuses in the form of certificates they could not redeem until 1945.
Laws regarding veterans changed in 1979 to pay pensions.
In July 1919, the United States Congress passed an act providing that a record of service for each soldier, sailor, and marine who served between April 6, 1917, and November 11, 1919, be created and furnished to the adjutant general of the individual states.
The service records for most World War I Army veterans were destroyed in a 1973 fire at the National Personnel Records Center of the National Archives (St. Louis). These records may be the only sources of information.
Might be in the Adjutant General's office, the state archives, or a museum. Some are available as microfilm collections in FamilySearch.org or as searchable databases in Ancestry.
Alfred H. Carrigan, Jr. World War I Service cards. Texas Military Forces Museum
Development of service cards:
There is no one source to identify where the service cards exist.
Selected record groups at the Delaware Public Archives:
World War I Servicemen Records. Delaware Public Archives Record Group: 1800.050
War history records of Delaware veterans who served from 1917-1919. Records show name and address of serviceman, identification number, date and place of birth, parents’ names and addresses, engagements or battles engaged in, citations of decorations conferred, particulars of death, if applicable, prior service information, current enlistment information, discharge date and identification number, overseas service dates, vital statistics concerning wife and children, if any.
World War I Army Service Record Cards. Delaware Public Archives Record Group: 1800.068
Statements of service cards and applications for victory medals for servicemen who participated in the U.S. Army during World War I. Statements of service include: serviceperson’s name, race, home address, place and date of birth, date and rank when drafted, rank and date of promotion, organizations and staff assignments, military bases stationed, military engagements participated in, wounds received, length of time served overseas, date of honorable discharge, percentage disabled and general remarks. Includes applications for victory medals. Creator: Delaware National Guard