dv said:

The last widow of the US Civil War soldier died in 2020.

This was Helen Viola Jackson, who married James Bolin in 1936, when she was 17 and he was 93. She was helping him with domestic chores and he offered to marry her as payment, as she would be eligible to receive his military pension. They never lived together and kept the agreement quiet, and when he died in 1939, she did not claim his pension.

Seems improbable but there you are.