Right, NessaUK,
I've had a look through the 1802 now, and although I cannot find the SURRY family name there then - perhaps he came from a nearby parish - there are several REYNOLDS households, all of whom could I suppose have been related in such a small place. And a very likely baptism date for your Mary REYNOLDS. Here goes:
In the household of William ANDREWS,bapt. 29-12-1717 (first marriage no details, second marriage 19-09-1780 - and presumably added later: died 23-09-1803)
Elizabeth (LORD, wid) his wife
Marian LORD her daughter
Thomas REYNOLDS her natural son, bapt. 12-10-1788
One can perhaps interpret this entry as Elizabeth either marrying a REYNOLDS first, or perhaps having an illegitimate son Thomas before she married a man called LORD, and then being widowed before marrying William ANDREWS. I think "natural son" usually infers illegitimacy.
So, this Elizabeth, I would say, was born a REYNOLDS, and may be part of an earlier generation of your family in Hinxton.
Now, in the second of two tenements, belonging to John BENSON of Whittlesford, with a garden of 2 rods and 8 and a half (poles?) were the following family:
Thomas REYNOLDS b. 24-04-1763, bapt. 24-04 1774, married 25-02-1788
Elizabeth (HUNT) his wife
William, bapt. 13-7-1788
Richard, bapt. 14-04-1790
Sarah, bapt. 25-12-1791
****Mary, bapt. 26-06-1799
Thomas HUNT, bapt. 25-11-1804
Grace REYNOLDS his mother, bapt 20-09-1730, (died 02-08-1803)
If this is indeed your Mary Reynolds she would have been 18 or 19 years old when she married Samuel Surry. And you have two more generations of Mary's family recorded in this Census - her father Thomas, and her paternal grandmother Grace
There are some more REYNOLDS entries, and I'll put them in my next post. This is getting quite long now...
Keith