I show Mary Jane Colbert Kincaid death in Coles Co. IL .
Her death cert gives DOB as 11/27/1848 which matches the census records. Death cert names her parents. It is indexed as Mrs John Kincaid Sr.

John was born in 1842 and they are both buried in Rosedale Cemetery in Oakland, IL

Mary Jane could not have been born in 1837 because her parents did not marry until 1840. I dont know where you got the date of birth for John Kincaid, but it is also in error.