Confusion and working together are expectedtraits of genealogy.Ages of Wm, Sr and Maryare very close to yours.Census are known to be wrong sometimes, soVa. Birth-state could be in error.
I’m not 100% that Wm P.’s 1st wife was Eliza.. The census was hard to read but I’m pretty sure it says Eliza.Also youngest child (son) name was hard to make out but think it was Joel C.
Marcia Gregory lived in Macedonia Iowa.With location, ages and time of marriage, I’mbetting that the Wm. Dinwiddie in 1880 censusis same Wm. P. Dinwiddie married Marcia.
1880 Census, Macedonia, Pottawattomie County Iowa
49-50 Dinwiddie, Wm.age 38Occupation farming,born Ohio
Dinwiddie, Eliza. wife, age 29.keeping house
Dinwiddie, Mary E, daughter, age 11
Dinwiddie, Sarah P. daughter, age 10
Dinwiddie,Phebe, daughter, age 4
Dinwiddie, Joel C ,son age 9/12
Dinwiddie, Wm. father, age 70born Va.
Dinwiddie, Mary,mother,age 66born Ohio
Probable 2nd wife ofWm. P. Dinwiddie
+Marcia Field Gregorym.. January 25, 1893
William Henry Dinwiddie, February 23, 1894 - August 27, 1926
I also have a Clara Moseley Dinwiddle,born December 22, 1869, Waterloo, Iowa, dau ofJames and Catherine (Moseley) Dinwiddie.
Clara is married to Hiram Kyle Devier(my paternal line).They lived in Mo. andhad several children.I don’t know if they connect to Wm. P. Dinwiddie.