Jo(h)anna Robins married John Fowler of the Royal Sappers and Miners at St Andrews Plymouth on 16 May 1823. He was a bachelor, she was a spinster. Their first child was baptised Mary Ann Wills Fowler in the following year in Launceston. They had several children, some were born in Ireland.
In 1841 they were back in Launceston, John's age gives a birth year of 1801 (rounded) and was not born in county. This matches with his birthplace of Woolwich, Kent and birth 22 Dec 1799, baptism on 13 Jan 1800. Joanna also has a birth year of 1801 and was born in County (Cornwall). The children with them seem to be recorded correctly where I can match with baptisms or later census records. This makes me fairly confident that Joanna was born in Cornwall between 1797 and 1801. Although Joanna was not literate (made her mark on marriage record), John was a surveyor and map maker working on the Irish survey, so would be quite literate enough to complete a census form accurately. Joanna died late 1841, so can't get information from a later census.
I'm trying to find a bit more about Joanna's parentage and to see where the "Wills" as the first child's middle name came from. It obviously isn't the mother's maiden name.
I think the most likely baptism is in Launceston in 1801 (Non-conformist) parents John and Grace.
I think the mother is Grace Hoskin who married John Robins at St Thomas by Launceston 16 Jan 1792.
Can anyone come up with a better alternative, hopefully solving the mystery of the Wills name.