Union Census Records
1890 Veterans Schedules
The 1890 Veterans Schedules were separate schedules of the 1890 Federal Census that were made of Union Civil War veterans or their widows. Confederate veterans were mistakenly listed as well. The records are also known as the "Special Schedules of the Eleventh Census (1890) Enumerating Union Veterans and Widows of Union Veterans of the Civil War". (NARA M123) (118 microfilm rolls)
A wiki article describing an online collection is found at:
1910 U.S. Federal Census
The 1910 Federal Census (NARA T624), asked if a person was "A survivor of the Union or Confederate Army or Navy".
1930 U.S. Federal Census
The 1930 Federal Census (NARA T626), asked if a person was "A veteran of the U.S. military or naval forces mobilized for any war or expedition" and "What war or expedition" they served in.
1940 U.S. Federal Census
The 1940 Federal Census, asked "Is this person a veteran of the United States military forces or the wife, widow, or under 18-year-old child of a veteran?" and "If child, is veteran-father dead?" and "War or Military" served in.