During the American Revolutionary War, he joined the Connecticut militia and served as a Private in his fathers Company. 
He first married on 30 Dec 1784 in Lebanon, New London County, Connecticut to Susannah "Susan" WILLIAMS, b.13 Jul 1764 in Lebanon, daughter of Lucy (WALWORTH) and Veach WILLIAMS of Lebanon. She was a second cousin of Chancellor WALWORTH of Saratoga Springs. She left several children when she died on 20 May 1792 in Lebanon Twp, New London County, Connecticut.
Eliphalet next married on 25 Aug 1793 in Franklin, Connecticut to Rachel Ann HYDE, the only daughter of Martha (WATERMAN) and Silas HYDE (or HIDE) of Norwich, Connecticut. 
About 1798 he moved his family from Connecticut to to Hardwick, New York
and his children were educated at Hartwick Seminary. Later he moved to Cooperstown, New York.
In 1835 he moved to Cadiz, Harrison County, Ohio where he lived with his son Chauncey Dewey. Eliphalet died on 04 Jan 1837 in Ohio.
a) Eliphalet DEWEY b.15 Apr 1786 Lebanon, New London Co, CT
a) Susan #1 Dewey b.1788 Lebanon, New London Co, CT d.04 Jul 1789
a) Susan #2 DEWEY b.31 Mar 1790 Lebanon, New London Co, CT d.18 Aug 1836 m. bef.1837 Jonathan SPRAGUE
a) Lucy Williams DEWEY b.21 Feb 1792 Lebanon, New London Co, CT b.21 Feb 1792 d.16 Mar 1848 m1+CAMPBELL d.26 Jul 1821 m2+Nathaniel MAYO b.1773 d.15 Mar 1845
b) Martha DEWEY b.1794 near Norwich, CT (died young)
b) Chauncey DEWEY b.27 Mar 1796 Cooperstown, NY, res: 1860 Cadiz, Harrison Co, OH, d.05 Feb 1880
b) Joshua Hyde DEWEY b.21 May 1797 Cooperstown, NY, d.1841
b) Henry DEWEY b.01 Sep 1800 Hartwick, Otsego Co, NY, occ: doctor, d.20 Jun 1831 m.1826 Eveline GAY
b) Harriet DEWEY b.1803 Hartwick, Otsego Co, NY d.25 Dec 1842 m. Feb 1837 Jonathan SPRAGUE
b) Silas Hyde DEWEY b.21 Apr 1806 Hartwick, Otsego Co, NY d.17 Mar 1864
↑ "United States Revolutionary War Rolls 1775-1783" FHL #830,306, NARA M246 for Eliphalet Dewey citing 10 Jan 1778 Connecticut; at FamilySearch accessed 21 Dec 2016.
↑ 3.03.1 North America, Family Histories, 1500-2000 available at ancestry.com citing "Hyde Genealogy, or, The Descendants, in the Female as Well as in the Male Lines from William Hyde" by Reuben Hyde Walworth, b.1788 d.1867 and published in 1864 in 2 volumes (with image included here).
1790 USA Census of Lebanon, Windham, Connecticut; FHL #568,141, NARA M637 _1, p248, for Eliphalet Dewey at FamilySearch accessed 6 Feb 2018.
Eliphalet Dewey on Find A Grave: Memorial #129194930 d.01 Jan 1837, buried Cadiz Union Cemetery, Cadiz, Harrison County, Ohio - headstone has a Revolutionary Soldier banner on it.
U.S. Sons of the American Revolution Membership Applications 1889-1970 SAR membership #79873 and available on ancestry.com.