The earliest Achurch baptisms in St Neots were in 1775, 1778 and 1780, children of Robert and Elizabeth, yeoman. Then none until Samuel starting baptising children in 1814.
It's possible that Elizabeth died in 1780 and Robert remarried Martha in 1781. The dates would make the chronology just about possible. BUT an Elizabeth Achurch aged 74 was buried in St Neots in 1812, which looks suspiciously like the widow of Robert who died in 1801. The parish register of St Neots needs checking to see if any additional information is given, eg yeoman, widow. There are also burials in St Neots of a Samuel Achurch age 56 in 1831 and Sarah Ann age 76 in 1858
In 1851 living in St Neots were John Achurch head 29 b St Neots, Sarah Achurch mother widow 70 b Rushden; Ann Achurch unmarried sister 34 b St Neots; Elizabeth Achurch unm sister 30 b St Neots. So this appears to show that the marriage that Suz found in Rushden is the right one.
Other baptisms in St Neots, children of Samuel and Sarah Anne were
12 Feb 1818 Mary
29 Aug 1819 Elizabeth
10 Jan 1820 Elizabeth
13 Jan 1832 John aged 9
David
