LizzieL – what a great catch!

How’d you do that? In fact, William’s occupation changes from labourer to shepherd, from the first to second (folio 430) entry. He would claim shepherd again in 1861.
And thanks, everyone, for your help on this.
There are three leading theories at this point: (1) he’s from Aston Tirrold; (2) he’s from Harrow; and (3) he’s from Harrold, Beds.
To test the Aston Tirrold theory (thanks Supermoussi) I’ve taken a very close look at the letter “H” vs. “T” in each of the three censuses. I think the 1851 census may support this theory as the first letter looks more like the other “Ts” than the other “Hs” if one had to choose. However, the 1861 census is a closer call. I think it looks more like an “H”, but a case can be made it is a “T”. My main problem is the 1871 census where it is, without a doubt, an “H” and not a “T”. Also against this theory is the lack of William Stones being born in Aston Tirrold at the right time (whereas there are more than a few in Harrow and Harrold).
As for theory #2, I do not think he was from Harrow. Only one of four entries have this and it seems likely someone said “Harold” but this particular enumerator heard it as “Harrow.”
So, in the end, I think it is most likely Harrold, Beds, despite the 1851 and 1871 censuses putting the parish in Bucks. The 1861 census just says “Harold” and includes what looks like a question mark – which gives me some comfort that I’m not the only one confused by this response.
Finally, as avm228 suggested, I have ordered the certificate from his second marriage, which will hopefully settle it. I’ll post the result.