There is a 20 yr. gap in the census records [1880 - 1900] as the 1890 census was burned in the 1920's. Add 20 yrs to everyone's 1880 age for the 1900 census.
I’m not related to any member of this family.
Andrew could not have been KIA in the CW as he would only be abt 14.
But he could have been killed from a 'stray shot', disease, or natural disaster.
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ILLINOIS did not issue death certs until 1915/1916; parents names are usually listed.