Hello,
The baptisms of John's son, Henry, it says John and Sarah were "of Theale", so it is possible that Sarah came from Englefield, Tidmarsh, Sulham etc. and they were married there. Theale itself at that time was in the Tilehurst Parish.
To add to what other people have said there was also a marriage in 1822 at Tilehurst between a John Barnes and Lucy Johnson who also appear to have had at least one child baptised and married there.
This might be a red herring and he is a different John b 1791 but he seems to be living in Reading in 1841.
A further confusion is that a John Barnes, widow, living with Henry and Amy in 1861 puts his age at 78 (1783) whereas a burial in Tilehurst in 1871 puts his age at 79. (1792).
Also that there are other children of a John Barnes being married at Tilehurst later in the century.
I had presumed at present for the lack of other evidence, that John Barnes was, as Artifis says, son of William and Susannah and that he married 3 times.
More work and certificates needed for this family, methinks.
Yours
Vicwinann