Frederick & Sophia are both enumerated in the same household in 1881, both unmarried.
He's a lodger and she's a domestic.
Then in 1891 they are together as man & wife, with 3 children age 9, 7 & 4.
So one might imagine a marriage pretty soon after 1881 Census...
However, it looks like they didn't tie the knot until late 1890, after those 3 children were all born:
FreeBMD MARRIAGE: Highworth, Dec Qtr 1890
Frederick HINDER and Sophia KEENE on the same page
(Highworth was the reg. district covering Swindon at the time - in 1889 it became Swindon)
1881: 3 Albion Terrace, New Swindon, Cricklade, Wiltshire
RG11- Piece: 2019/ Folio: 88/ pg27
Head: John HEAD 39?, Striker, b Devonshire
Wife: Mary HEAD 40, b Cornwall
Lodger: Tho's SMITH 30, unm, Striker, b Leeds Yorkshire
Lodger: Rich'd BINNIE? 23, unm. Brick moulder, b Somersetshire
Losger: Cha's LINTON 15? (45?), unm, Mechanic, b Plymouth, Devon
Lodger: Fred'k HINDER 31, unm, Labourer Factory, b Ashton Keynes, Wilts
Servant: Sophia KEENE 23, unm, Domestic servant, b Leigh, Wilts
1891: 57 Mill Street, New Swindon, Cricklade, Wiltshire
RG12- Piece: 1584/ Folio 98/ pg40
Head: Frederick HINDER 40, General Labourer, b Ashton Keynes
Wife: Sophia HINDER 34, b Cricklade
Dau: Emily K HINDER 9, b Swindon
Dau: Harriett L HINDER 7, b Swindon
Son: Frederick R HINDER 4, b Swindon
1901: 21 Haydon Street, Swindon, Wiltshire
RG13- Piece: 1906/ Folio: 150/ pg4
Head: Fredrick HINDER 52, General labourer Railway Works, b Ashton Keynes
Wife: Sophia HINDER 43, b Leigh Wilts
Dau: Emily K HINDER 19, unm, Laundress, b Swindon
Son: Fredrick HINDER 14, Errand Boy (Grocers), b Swindon
Dau: Frances HINDER 9, b Swindon
Dau: Mary A HINDER 6, b Swindon
Son: John S HINDER 4, b Swindon
(I think daughter Harriet L HINDER is in Service, in Bath, Somerset)
BIRTH: Emily Kate KEEN - Jun Qtr 1881
BIRTH: Louisa KEENE - Sep Qtr 1884 (Think this is Harriet L - perhaps "Harriet" was added later at baptism?)
BIRTH: Frederick Robert HINDER - Jun Qtr 1886
Sophia must have been due to give birth to Emily at the time of the 1881 census (I can't see Emily elsewhere in 1881 as a newborn).
Cheers
AMBLY