Witnesses to the marriage were Albert Margetts and Elizabeth Stroud.
James is identified in the register as a 43 year old bachelor, Eliza a 40 year old spinster.

The Parish Baptism and Marriage registers indicate that both children from this marriage were born out of wedlock.

James is identified in the 1871 census for Oxfordshire and North Berkshire as living at Banbury with Eliza and firstborn daughter:
James Knibbs abt 1846 Woodstock Head Banbury Oxfordshire
Eliza Knibbs abt 1850 Gloucestershire Wife Banbury Oxfordshire
Eliza Ann Knibbs abt 1871 Oxfordshire Daughter Banbury Oxfordshire
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James appears in the 1881 census living with his wife and children at Browns Lane, Woodstock, Oxford, England:
James KNIBBS Head M Male 32 Woodstock, Oxford, England General Dealer
Eliza KNIBBS Wife M Female 30 Gloucester, Gloucester, England
Eliza A. KNIBBS Daur Female 11 Oxford City, Oxford, England Scholar
William KNIBBS Son Male 9 Oxford City, Oxford, England Scholar
Thomas KNIBBS Son Male 7 West Woods, York, England Scholar
Agnes KNIBBS Daur Female 4 Oxford City, Oxford, England
Harry KNIBBS Son Male 5 m Woodstock, Oxford, England
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The 1891 census for Oxfordshire and North Berkshire shows James' wife Eliza living at Woodstock with just two children.
Eliza KNIBBS 41
Thomas H 16
Agnes 13

It also shows that James was living a few doors away from Eliza with their younger son Harry, then aged 11 (although listed in the census as Henry)
James KNIBBS 45
Henry 11

This indicates that James was either away from home during the census or alternatively, he and Eliza had separated and were no longer living together as man and wife?

I Understand from Trevor Knibbs, a descendant of this line, that James and Eliza split up in later life but did not divorce. It is thought that both continued to live in Woodstock, and that James lived to be one hundred. Eliza may have died in the 1920's.
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The 1901 census shows James aged 53 living alone at Home Farm, Woodstock and Eliza living at Oxford Street, Woodstock with daughter Eliza and sons William and Harry:

James KNIBBS, 53, Pork Butcher, Oxon Woodstock
He is identified as married.

Eliza KNIBBS 51 Glous Gloucester Oxon Laundress
Eliza A KNIBBS 30 Oxon Oxford Oxon Laundress
William J KNIBBS 29 Oxon Oxford Oxon Carrier
Harry KNIBBS 20 Oxon Woodstock Oxon Fishmonger

Also living with Eliza was her niece Elizabeth Daniels, 18 Laundrymaid Domestic from what appears to be Glamorgan(?)

Eliza's father was Thomas Greenland, a labourer. I believe it is this Eliza who was born in q4/1849 although her age on several census returns indicate she was born 1850/51.

John died in November 1886 aged 3 years.

Eliza appears in the 1891 census living at Caterham, Surrey, England.

Name Relationship Age Gender Birthplace
Thomas W Gunton Head 47 Male Chatteris, Cambridgeshire
Emily Thersa Gunton Wife 29 Female Longford, Middlesex
Grace Gunton Daughter 5 Female Chiswick, Middlesex
Philip Hy Gunton Os 2 Male Stanwell, Middlesex
Octavia Bertha Garnham Visitor 36 Female Plumstead, Kent
Eliza A Knibbs Servant 20 Female Oxford, Oxfordshire / Oxon
Mary Jane Wilson Servant 25 Female Newcastle, Northumberland
Town: Caterham, Ecc. Parish: Caterham, Civil Parish: Caterham, County: Surrey
Registration: Godstone, Godstone, 3
Source: PRO/National Archives Reference # RG12/582 Folio 68 Page 50
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Understood from Trevor Knibbs that Eliza Ann didn't marry, and that she died in Woodstock.