I'm unsure if the Simpson W. in my data base is the same as your Simpson W., although they are possibly the same because they are about the same age and yours gives his birth state as TN in 1880. I don't even know that the Simpson in my data base went to TX, but some members of his family did so.
In 1860, S. W. or S. M. Alexander was living with his sister Sarah and brother-in-law Lewis Lafon in Ellis County, TX. The age, 27, actually fits Simpson's brother Sampson as Simpson would have probably have been a couple of years older, and Simpson had married in 1852 while the S. W. on the census appears single (or widowed?).
They are apparently not members of my family, but I have done some research on them to separate the various Alexander tribes in my west TN area. If this lead appears promising, let me know and I'll give more information.