Was a resident of Kingsthorpe parish, Northamptonshire, at the time of both marriages.

In 1828, John and his family (with children, Joseph, Thomas and Ann), moved from Kingsthorpe to Moulton, but based on the 1841 census, by that time they had moved back. [865], [877]

No John CHOWN found in the baptism register of Moulton Parish, 1790-1804 (see book cited by Source [846] Also browsed images of Moulton register 1795-1799). It does, however, show baptisms of children born to a Henry and Anne CHOWN:
Elizabeth, 01-APR-1791
Sarah, 19-AUG-1792
Alice, 11-MAY-1794
Mary, 11-MAR-1796
Hannah, 25-APR-1798
William, 11-APR-1800
Edward, 22-AUG-1802
Thomas, 25-DEC-1804
And based on these dates, this would appear to correspond to the marriage of Henry CHOWN of Pitsford and Ann LANSBURY of Guilsborough, 11-JAN-1790. [994]

Perhaps John was not born in Moulton, or was not baptized (or was much later).

Not found in Northamptonshire Birth & Baptism Index CD. [4646]

19-MAR-2016: Searched Ancestry.com: Northamptonshire, England, Church of England Baptisms, Marriages and Burials, 1532-1812. No records found for a John CHOWN born 1795-1799 in Moulton, nor marriage in 1821 (marriage was in Kingsthorpe). That collection includes the Moulton register book covering 1740-1799.
Further suggesting his birth was not in Moulton, but a search of all Northamptonshire also fails to locate a baptism for John CHOWN in the 1798 timeframe. The only one found was baptized in Braunston parish, 29-MAY-1808, with parents Joseph & Sarah. Which would have made him 10 years younger at death.

Searched Ancestry.com: England & Wales, Non-Conformist and Non-Parochial Registers, 1567-1970. No matches there either. (including RG4, Piece 3361, The Register Book, Baptist Chapel, Moulton, Northamptonshire).