Hi - I'm looking for information on William Thomas LEHEW, b. 23 Jul 1853 in Ohio and his wife Rebecca b. abt 1853- possibly Rebecca Day (Diantha) CROGHAN. They were married Jan 1874 in Benton County, Iowa. I don't have any more on her or him.

Basically I am trying to prove my relation to them for the DAR and I have nothing, except my grandfather's birth cert. So any suggestions on where to find a birth cert, will, marriage or when he died, etc. This is my great-great grandparents.
thank you!