Here's a breakdown of what's in which area (At the time of 1841 census) ... you have to remember that on the census it can be pot luck as to whether it says London or Middlesex and county & borough boundaries in & around London were constantly changing!!
 
Districts in MIDDLESEX -
 
    Barnet, Edmonton, Brentford, Staines, Uxbridge, Finsbury, Enfield, Hendon, & Kingston (Nowadays these are Essex/Surrey!!)
 
Districts in LONDON -
 
    Barnet, Edmonton, Clerkenwell, Whitechapel, Bermondsey, Bethnal Green, Brentford, Kensington, Bromley, Dartford, Lewisham, Sevenoaks, Camberwell, London City, Croydon, Richmond, Wandsworth, Greenwich, Guildford, Hambledon, Hackney, Holborn, Strand, Islington, Lambeth, Marylebone, Medway, Newington, Poplar, Romford, West Ham, Rotherhithe, Shoreditch, Southwark, St Giles, St George, St George In The East, St luke, St Martin, St Pancras, St George Hanover Square, Stepney, Strand & Westminster.
 
Remember, this only relates to the 1841 census - it changed year to year as to what is where, quite a few of the above are now in Surrey, Essex & Kent.
 
London is constantly evolving even today where borough/district boundaries are still changing!
 
The best way to go when searching online is to aim for Middlesex if they're not born in the City and then if it doesn't come up with results put London in and you may just find them!!
 
London is made up of many invisible boundaries that only a true Londoner can understand, my brother lived in London for a while and one of his addresses began life in London, then moved to Surrey and changed borough 3 times and that was just 15yrs ago!!