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1871 census:
Class: RG10; Piece: 49; Folio: 40; Page: 2
29 Queen Street, Kensington
Parsons, Richard Head M 42 Messenger b Market Bosworth, Leicestershire
Parsons, Louisa Wife F 49 b Sydenham
Parsons, Louisa J Sister-in-Law F 6 b Park Lane, London
And, for the record, their marriage:
June qtr 1851
Leicester district vol 15, page 154
Parsons, Richard
+ and on the same page +
Cooper, Sarah Louisa
If you can't see this on a Parish Register (which are from C of E churches) then perhaps they were Catholic, non-Conformist, or married at the Register Office?