I did a quick search at Familysearch.org (LDS) site and here is what I found and didn't know if you already had this. There was no source given so use this as a guide and follow through with census records:
Sarah Thomas Partlow born 1837, Chippewa, Isabella, Michigan
Parents: David Partlow and Sarah Hire she married Stephen Thomas, Dec 23 1858, Iona Mich she was 21 yrs of age and he was 28 yrs of age
she married William S. Abbott July 1901, Mount Pleasant, Isabella, Mich he was born about 1827, NY son of W.S. Abbott and Elizabeth Thomas. William died May 1, 1911
3rd Marriage to James Bearer, October 2, 1916, Mount Pleasant, Isabella, Mich
he was born 1840 in Ohio and died Oct. 20, 1918 son of Notsil Bearer and May J. Conklin
I have Partlow ancestors also but they were St. Clair County Michigan and not connected to yours. Yours may have come out of Ontario Canada but I am not sure, you would have to do some more searching. In the mean time I will look at Ancestry.com for you.