In the UK 1881 census in England the Ollington variant of the name seems to predominantly be found in the county of Suffolk in England, more specifically close to the town of Bury St Edmunds.
This is clearly illustrated by the 1881 census population map:
The numbers of Ollingtons recorded in each of the England and Wales census returns 1851-1901 are, respctively:
The results of the 1851 census seem to be anomalous but closer inspection reveals significant occurencies of mis-recording and mis-transcription.
The disppearance from Middlesex in the 1871 census is caused by a switch from Ollington to Hollington of all Ollingtons recorded in the 1861 census. These are all believed to be descended from two Ollington brothers who moved from Suffolk to the London area in the late 17th/early 18th centuries and settled in Bromley, Middlesex. The reason for the name change is uncertain but may simply be due to the fact that this area was becoming overrun by the expanding east-end of London and Hollington presumably sounded 'posher' than Ollington (as the tendency of the local accent was to drop 'the H')