Check the source I have attached to this John Harmon Revolutionary War John Harmon. The source comes from the Genealogy Library of Greene County, TN. It has this John Harmon's will and gives the details of his off spring. The Jacob that is his son attached is a different set of Harmons. There are 4 different sets of Harmons in Greene County that settles at the same time. Each one has the same names and lived in the same general area of each other and they named their off spring the same and the birth dates are within a couple of years of each other, so it gets confusing. To top it off they intermarried into each family.
This John Harmon b.1751 VA-d 29 December 1838, Greene Co., TN; His son, Jacob 1772-d. unknown Greene Co., TN; m. 31 Aug 1811Greene Co., TN to Polly Pratt.) 2.Margaret b.abt. 1793-d. 15 Sep 1860 [said to be from Family Bible; m. 24 Jul 1810 Greene Co., TN to Clement Reynolds 3. John Jr. b. 29 Nov 1783- Apr 1854 Greene Co., TN; m. 23 Mar 1824 Greene Co., TN to Anna Monger4.) Peter L. b. 18 Apr 1785 [Tombstone]-d. 3 Aug 1870 [1812 Pension] Greene Co., TN; m. 24 Feb 1820 [Family Bible] Greene Co., TN to Elizabeth “Betsy” Bowman5.) Milly b.ca.1786-d.ca.aft. 1855 MO; m. 15 Nov 1803 Greene Co., TN to Thomas Perry m. #2 20 Feb 1823 Greene Co., TN to David Brown Sr.6.) Benjamin b.abt 1787-d.bef. 2 Jan 1828 [per estate]; m. Fanny Pratt 1777.
The Jacob that you have attached as his son here is my set of Harmons not the correct one. I have not been on here in a while so I don't know when this was compiled or how it was added to John because we have no idea who his father is,we only know he came from PA along with the Messimer family, but we know its not this John's son.