Zebulon Smith was not your ancestor. I haven't even been able to support your belief that Elon and Nancy A (Ella Smith) Boyce are the parents of your grandmother Myrtle C Boyce.
Nancy's family never lived in Lenawee Co., MI.

1850 U.S. Census- Virginia > Lee > District 31, page 144(image 146), family 991
Richard Gilliam 54 VA farmer
Rosannah 46 NC
Harriet 17 IN
Elias T 14 IN
Rebecca J Gilliam 9 IN [future mother of Nancy A Smith]
Rosannah 7 VA
family 192
William P Gilliam 22 NC
Eliza 18 VA
Richard 1 VA

1860 U.S. Census- Iowa > Winneshiek > Decorah, pg 31, family 220
Israel Smith 24 NY laborer
Rebecca J 20 IN
Nancy E 2 Iowa
unnamed baby girl 1 mo (Apr 1860) IA
Rosa Gilliam 54 NC (mother-in-law)
Rosanna E Gilliam 16 VA

1870 U.S. Census- Iowa > Winneshiek > Decorah, pg 33, family 216
J K Smith 36 NY cooper
Rebecka J 29 IN
Nancy A 11 Iowa
Alice M 9 Iowa
J. K. 8 male Iowa (Kingsbury)
L. B. 4 male Iowa (Leslie)
Florence A 1 Iowa

1880 U.S. Census- Michigan, Osceola, Richmond, e.d. 223, pg 23,
family 314-
Elon Boise 30 NY NY NY day laborer
Ella 21 Iowa NY VA
Jennie 3 MI NY IA
Alice 1 MI NY IA

family 316
Isrel K Smith 40 NY NY NY day laborer
Rebecca 39 IN NC NC
Kingsbury 16 Iowa NY IN
Leslie 14 male Iowa NY IN
Florence 11 Iowa NY IN
Frankie 9 male Iowa NY NY [sic]
Della 7 MI NY IN
Wilton 4 MI NY IN
Samuel 7/12th MI NY IN