1a.  Allen L. Potts.  Marion County, Ohio, Probate Court Marriage Records, Vols. I-XII, 1824-1902 (online at Heritage Pursuit):

Elliot, David H.	Armstrong, Mary Ann	3/30/1854	JP S.N. Groswold
Smith, David	Elliott, Mary A.	10/23/1859	JP P.N. Francis

Has our widow remarried?  The J.P. is Philander K. FRANCIS, Mary Ann (ARMSTRONG) ELLIOTT's brother-in-law.

1b.  LDS.  Family Search: Internet Genealogy Service: IGI - International Genealogical Index (online at FamilySearch.org).

David H. R. ELLIOT Spouse: Mary Ann ARMSTRONG Marriage: 30 Mar 1854, Marion, Ohio Source: Marriage Records, 1824-1964. Ohio. Probate Court (Marion County)

2.  1860 Census Every-Name-Index/Images (online at Ancestry.com):  David not found, as expected, but I can't find Mary Ann, either, at least not as Mary ELLIOTT.  I made a cursory search for a David & Mary SMITH, but they are not found in Marion County, so after some searching elsewher, gave up.

3.  Paul J. Midlam & Barbara Midlam.  1985.  Marion County, Ohio, Cemetery Inscriptions (online at Heritage Pursuit):

ELLIOTT, O.H.R.

d. Aug 23 1859 Aged: *27y 2m 19d

Waldo [Cemetery]

Waldo [Twp.]

4.  Birthdate calculated using Ben Buckner's Birthdate Calculator.

Name	Deathdate	Age at Death	Result
D.H.R. ELLIOTT	23 Aug 1859	19d 2m 27y	4 Jun 1832

5.  WorldConnect / Ancestry World Trees (online at RootsWeb.com/Ancestry.com).