Mary Hooker and Robert Bell had a son, Erastus Porter Bell.
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1850 U.S. Census, 23rd Civil District, Wilson County, Tennessee (Ancestry.com Images Online, image 298))
Enumeration Date: Line: 23
379/379 Robert Bell, 45, b. Tennessee
Sarah, 32, b. Virginia
Erastus, 17, b. Tennessee
Sarah, 8, b. Tennessee
Jane, 7, b. Tennessee
Tennessee, 5, b. Tennessee
Robert, 3, b. Tennessee
Samuel, 2, b. Tennessee
George, 1/12, b. Tennessee
James Hancock, 12, b. Tennessee
It would appear that Sarah is the second wife of Robert Bell, judging by the younger ages of Erastus' siblings. Erastus' mother, Mary Hooker, must have died before 1842. And, how does James Hancock fit into this family?
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In searching Ancestry.com for Erastus Porter Bell:
Erastus Porter Bell (b. 1833, d. 1933); m. Harriett Barber (b. 1877, d. 1899)