Working theory: David Bay was the father of both Cyrus Bay and Mary Ann Bay.

1827 Birth of Son Cyrus:340 "Father's name in full: David Bay; father's birthplace: Pennsylvania"

1840 U.S. Census:2017 Are Mary Bay and Cyrus Bay siblings? Relevance of this census record not proven.
Wayne County, Ohio (Plain Township)
Head of Family •• David Bay
Males 10-15 •• 1 << Possibly Cyrus, age 12 ??
Males 40-50 •• 1
Females under 5 •• 1
Females 5-10 •• 1 << Possibly Mary, age 10 ??
Females 15-20 •• 2
Females 20-30 •• 1

Evidence of Relationship:

1) Cyrus Bay’s father was David Bay. (Evidence:340 Cyrus Bay death certificate).

2) Mary Ann Bay married Benjamin Crull in 1847 in Wayne County, Ohio. (Evidence:1750 Wayne County marriage record).

3) Samuel Crull, oldest son of Mary Ann Bay and Benjamin Crull was born in Porter County, Indiana, in 1848. (Evidence:1760 Samuel Crull death certificate).

4) Cyrus Bay living in Porter County, Indiana, by 1850. (Evidence:173 Marriage in Michigan to Lucinda Bay, resident of Porter County, Indiana, per Cyrus Bay Civil War pension declaration).

5) The Crull family settled in Hanna Township, Henry County, Illinois and raised their children, while the Bay family resided in Wheeler, Porter County, Indiana. (Evidence: 1860,416 1870,1297 and 1880417 census records in Porter County for the Bay family; 18601728 and 18701731 census records in Henry County, Illinois for the Crull family).

6) Lora Arecelia Bay, daughter of Cyrus Bay, married Marquis de Lafayette Crull, son of Benjamin Crull in Henry County, Illinois in 1878 and resided there in 1880. (Evidence:1736,1729 Henry County, Illinois, marriage record; 1880 U.S. census).

How did these two individuals from different states meet and marry unless there were a connection between the families? My working theory would mean that Lora Arecelia Bay and Marquis de Lafayette were first cousins. This couple had one son, who died at birth.