i can only find in 1851 census mary costain age 28 with costains in arbory this must be her
1851
john costain age 70 head born 1781
mary costain age 59 sister born 1792
alice costain age 57 sister born 1794
mary a costain niece age 2
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in liverpool site i found
mary caton born jan ist 1823 to john caton and elizabeth alexander she wasnt christend till 1932 st johns old market liverpool