The last surviving civil war vet died on August 2 1956 at the age of 109.
That was the last Union veteran. Interestingly the last confederate widow didn’t die until 2008 (when young married a very old vet)
https://en.m.wikipedia.org/wiki/American_Civil_War_widows_who_survived_into_the_21st_century#:~:text=Alberta%20Martin%20(née%20Stewart%3B%20December,Civil%20War%20soldier%20produced%20offspring.