I am unable to find a record of his death, but she is called a widow in the 1900 and 1910 census, still in Ringgold County.
I did locate two sources for their marriage record, which you may or may not already have:
Illinois Statewide Marriage Index, 1763–1900
http://www.ilsos.gov/GenealogyMWeb/marrsrch.htmlGroom: LEWIS, THOMAS
Bride: REYNOLDS, ANN M
Date: 1865-12-25
Vol./Page: C/ 14
County: WARREN
__________________________
Illinois Marriages, 1851-1900
http://bit.ly/h4AA4qName: THOMAS LEWIS
Gender: MALE
Spouse Name: ANN M. REYNOLDS
Marriage Date: DEC 25, 1865
Marriage County: WARREN
Comments: This record can be found at the County Court Records, Film # 1377920 - 1377922