I think I found him in 1900 living in Bad Bluff, Henderson, Illinois. He is age 70 and apparently remarried abt 1883 to Nancy J. age 65. He is living next to William Cattison age 66. The census has Ira's birthdate as Oct 1829. Ira and Nancy have a daughter Clara A. born Dec 1885. Henderson county is where Mary and Ira were married in 1854. I still can't locate him in 1850 but will keep trying.
FURNALD, FREDCASTEEL, ADALINE MAY11/01/1898 FURNALD, GEORGE NHALL, SUSIE BEATRICE10/17/1893 FURNALD, IRACATTERSON, MARY M12/04/1854 FURNALD, MARSHALLFERRELL, SARAH09/27/1866 FURNALD, WALTERRYASON, MAUDE ALMA01/20/1896
I saw a land grant for a Mark Furnald in Illinois for his service in 1812. But no Marks appear in the census for Illinois prior to 1850. There are 2 Marks in Kittery in 1810 and 1820. Too bad we don't have Ira's middle name.