This is actually a multi-state and multi-generational rat's nest. Best to start with the first generation and take it one step at a time.
Seth Tarr Mitchell was born in Litchfield, Kennebec County, Maine on 19 May 1818. His parents were Joshua Mitchell and Nancy Tarr. Since only the heads of households were named on the 1840 census, I can't be sure, but it looks like Seth was still at home with his parents in 1840.
A Seth T. Mitchell allegedly married a Mary E. Bright on 19 October 1844 in Johnson County, Indiana:
http://marriage-divorce-records.mooseroots.com/d/c/Seth-MitchellAnd in 1850, there was a Seth T. Mitchel, merchant, age 37, born in Maine and living in Franklin Twsp., Johnson County, Indiana. His wife was named Mary E. There was a son Emerson Mitchel and two other children, Mary L. Bright and Septimus G. Bright, presumably step-children. [It is worth noting that Emerson was a fairly common name among the Maine Mitchells].
http://www.rootschat.com/links/01gto/Question: Does anyone have access to the original Indiana marriage records and, if so, is there anything to confirm that the Indiana Seth Mitchell was the man who was born in Litchfield, Maine?By 1860, Seth Mitchell seems to have abandoned Mary and Emerson. They were still in Indiana [Septimus had died and Mary L. Bright had married] but Seth seems to have gone to Wisconsin and acquired a different wife?, though he didn't actually marry her until 1867.
http://www.mocavo.com/1860-United-States-Census/126207/005165841/686#row-5http://www.mocavo.com/1860-United-States-Census/126207/005171801/93#row-11https://familysearch.org/ark:/61903/1:1:XR2W-PQZQuestion: After 1867, there is no further sign of Seth Mitchell. When and where did he die?