John Horner and Mary Ann Clarkson

St Anne, Limehouse - Entrance
cc-by-sa/2.0 - © John Salmon - geograph.org.uk/p/4559397

John Horner (bap. 16 Nov 1794 in Impington, Cambridgeshire), son of John Horner and Elizabeth Charles, purportedly married Mary Ann Clarkson on 20 Oct 1816 in Tower Hamlets, but I've yet to see a record or listing that confirms this. 

Records do show that John and Mary Ann had five children: 

1. Eliza Horner b. 22 Jun 1817, bap. 20 Jul 1817 in St George in the East Church, Cannon Street Road, Stepney
2. Elizabeth Horner b. 20 Nov 1819, bap. 14 May 1820
3. Samuel Horner b. 13 Apr 1822, bap. 26 May 1822 
4. Sophia Esther Horner b. 30 Jun 1824, bap. 19 Sep 1824 
5. John James Horner b. 27 Jun 1828, bap. 17 Aug 1828

At the time of Eliza's baptism in 1817, John Horner, Shoe Maker, and Mary Ann were listed as living in Terling Street, St George in the East. Elizabeth, Samuel, Sophia Esther and John James' baptisms all took place at St Anne, Limehouse.

In 1841, John Horner (45) was living in Caroline Street, Stepney (which runs down to Shadwell, between Ratcliff and Limehouse). In the household were Samuel Horner (20), John Horner (12), Mary Horner (50), Eliza Dennis (24), Elizabeth Horner (21), Eliza Dennis (15)*, Matilda Dennis (3) and Sophia Horner (17). From this we can only conclude that Eliza Horner had married someone with the surname Dennis, however, I've been unable to find a record of the marriage. For the second Eliza Dennis* to be 15, she would have to have been the daughter of the missing husband by a previous partner of his, though probably more likely is that this is an error in the transcription: perhaps she could have been 5 years old.

In 1851, John Horner (56) Carman (drove a vehicle used to transport goods), birthplace in Over, Cambridgeshire, was living in White Horse Street, Stepney with wife Mary Ann Horner (66) from St Lukes, Middlesex; Sophia Esther Horner (26) born in Limehouse, Middlesex; Eliza Dennis (33) Dress Maker, born in St Georges East, Middlesex, listed as Married - no sign of her husband here nor previously in 1841 - and granddaughter, Matilda Dennis (13) born in Poplar, Middlesex.

"White Horse Street was the main street of the medieval village of Stepney, centred around St Dunstan’s Church. Until the nineteenth century, although there were buildings along White Horse Street itself, the surrounding area was mainly open fields." [Source]

On the marriage certificate for son John James Horner to Mary Ann Louisa Howard at the church of St Peter, on 23 Feb 1851, John James occupation is also listed as Carman, while John Horner's occupation is listed as Coal Merchant. Samuel Horner, on subsequent records, was also described as a Coal Porter/Carman. 

In 1861, Mary Ann Horner (76) Widowed, was living in the household of her son-in-law John George Gilpin (married to Elizabeth), in Suffolk Street, Poplar.

John Horner, therefore, must have died between 1851 and 1861, most likely, in 1853, when there is a death of a John Horner with age estimated as 61, in the registration district of St Mary Newington (Southwark). Son Samuel Horner was later found in Camberwell, adding credence to finding him south of the river. 

Mary Ann Horner died at 82, in 1866 in Poplar (Volume 01C Page 839).