Possibly one of the four daughters:
.  Christina ELY, b. 28 Feb 1790, PA; d. 6 Feb 1825, Morrow Co., OH; bur. Mound (Foust) Cemetery, Morrow Co., OH; m. John FOUST (b. PA).

1.  Family Quest Archives:  Ohio Federal Census 1820:  Clermont, Darke, Delaware, Jackson, Mercer, Pickaway, Pike, and Trumbull Counties.  Heritage Quest CD M33-89 (extracted by Diana Gale Matthiesen):

1820

OH

Delaware Co.

Sunbery Twp.

p. 110

Michael Ely

000001-00001-0000

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	45 or over	in or bef. 1775	= Michael (b. ca. 1750)
1 female	45 or over	in or bef. 1775	= Christina (b. 1754)

Living eight doors down from his son, Peter ELY.  They are the only ELYs in the county. 

2.  Census Index:  U.S. Selected Counties, 1830 (Broderbund CD-315):  not found, as expected.

3.  Anon.  1880.  History of Delaware [County] and Ohio.  O.L. Baskin, Chicago (online at Heritage Pursuit):

p. 180	CHAPTER II... SETTLEMENT OF THE COUNTY BY THE WHITES...
p. 194	In the same year as given above (1807), settlements were made in Trenton Township... John Culver, Michael Ely and their families were the first settlers north of Culver's Creek, and located in the settlement in 1809.  Shortly after them John Williamson came and bought land of Ely, and during the year married his daughter Rosanna...
p. 587	CHAPTER XXVII. TRENTON TOWNSHIP... MANY of our elderly readers will readily remember the time when a large portion of the east half of the county was known as Sunbury Township.  It was the third township created after the organization of the county and dates back to June 16, 1808... it was whittled off... to what is now Trenton Township...
p. 589	The first settlement made north of Culver's Creek was by John Culver and Michael Ely.  They are noticed among the arrivals of 1809.  Not long after them came John Williamson and bought land from Ely.  He was a bachelor when he came to the settlement, but, sometime during the year 1810, he married Ely's daughter, Rosanna.  Their son, Madison Williamson, is reported as the first birth in the township...

4.  The Raymond Martin Bell Anthology.   "The Families of George Ealy, East Finley Township, and Michael Ely, Buffalo Township, Washington [County], Pennsylvania" (online at the Washington County PAGenWeb site).  Gives children as Catharine, Peter, and Rosanna, "plus four daughters."  Says 1790 census shows Michael with one son under 16 and five daughters.  Went to Cardington [Morrow Co.] in 1822.

5.  WorldConnect (online at RootsWeb.com).

6.  Messages in the Ely Family Genealogy Forum (online at GenForum.com).

7.  Query at the Morrow County OHGenWeb site.