This is all I could find. 10-18-1901 Mt Ayr, Ringgold Co IA Annie D GREGG b 1873 Hanson MO d/o Milton H GREGG/Susanna DAY m. Clay EWING s/o John EWING/Caroline ROSS
6-24-1885 O P GREGG m. Sarah Jane ROUCH, Worth Co MO
Kenton Felt GREGG b 6-20-1860 OH; d 3-1-1952 Grant City, Worth Co MO, bur Kirk Cem, Allendale MO; parents Milton H GREGG/Susana DAY; w/Nellie Bell ALLEN
Since parents Wm b 1795 & Nancy GREGG b 1799 were b in PA, they may have married there.There is a Wm m to Nancy CLARK, 12-20-1822 Harrison Co OH.Family is listed GRAIG 1850 Meigs Co.
There were several Israel DAYs m in Belmont, but yours wouldn't have been old enough to be any of them.I note his name is Joel 1880 census. 1860 Meigs Co his wife is Catherine.Couldn't find the family 1850.