I looks like sometime between 1875-1878, he moved on to Ill, and his wife Clara moved back to New York to live with a cousin (1880 US Census).
I have been told that, it is thought that he at some point when west into Indian Terrritory and did not come back or was killed. Some said he was part of Custer's Last Stand, but he is not listed as one of the dead or wounded there,as reported in the Bismarck (Dakota Territory) "Tribune", dated 6 July 1876.
These are the documents from Ancestry.com that I have found so far. Still would like to find what happed to Melissa and the two younger children, where Spencer Thomas was in the 1865 state censuses, the 1870 US Census, the 1880 US Census, and when he died and where. Did he die in Henry County Illinois or did he move on again?
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Source Citation: Year: 1850; Census Place: Lenox, Madison, New York; Roll: M432_526; Page: 186B; Image: 377.
Source Citation: Year: 1860; Census Place: Lenox, Madison, New York; Roll: M653_781; Page: 711; Image: 212; Family History Library Film: 803781.
Source Citation: Year: 1880; Census Place: Wawayanda, Orange, New York; Roll: 912; Family History Film: 1254912; Page: 406D; Enumeration District: 047; Image: 0190.
"Minnesota Marriages, 1849–1950." Index. FamilySearch, Salt Lake City, Utah, 2009, 2010. Index entries derived from digital copies of original and compiled records.
|Groom's Name:||S. P. Kilts|
|Groom's Birth Date:|
|Bride's Name:||Ida Slater|
|Bride's Birth Date:|
|Marriage Date:||25 Dec 1878|
|Marriage Place:||Lyon, Minnesota|
|Groom's Father's Name:|
|Groom's Mother's Name:|
|Bride's Father's Name:|
|Bride's Mother's Name:|
|Groom's Marital Status:|
|Groom's Previous Wife's Name:|
|Bride's Marital Status:|
|Bride's Previous Husband's Name:|
|Indexing Project (Batch) Number:||M74631-5|
|Source Film Number:||1255713|
|Reference Number:||Bk a p172|
Source Citation: Year: 1880; Census Place: Dunn, Otter Tail, Minnesota; Roll: 628; Family History Film: 1254628; Page: 77A; Enumeration District: 152; .
|Name:||S P Kilts|
|Titles & Terms (original):|
|Residence:||Dora, Otter Tail, Minnesota|
|Estimated Birth Year:||1852|
|Place of Birth:||New York|
|GSU Film Number:||000565794|
|S P Kilts||M||43y|
|Angy May Kilts||F||9y|
Source Citation: Year: 1900; Census Place: Dora, Otter Tail, Minnesota; Roll: T623_779; Page: 2A; Enumeration District: 156.