When I grew up Chelsea were still a bit fashionable a sort of MU of the South, but they won little and spent 9 years in Division 2 (now Championship). So there was always odd Chelsea fans all over the country. At Boro games you get Scottish Chelsea fans and there has been a Chelsea flag saying Barrow. When I lived in South London, Chelsea was probably the best supported team even though they were struggling (1988). I got the impression a lot had moved out of places like Lambeth and Battersea (that had a lot of early Victorian slums, but you could easily get to Chelsea ground from) since the London Council has been building new Council houses for the 1930s onwards on what was the edge of London then, so in places like Carshalton, Merton, Sutton, Addiscombe (in 1960s), Kingston (where there were a lot of aircraft factories). You would sometimes get pocket of council housing in quite posh areas of SW London like say Ham and that would be solid white working class back in the 1980s and into football when football was unfashionable, these clumps would be solid Chelsea. Chelsea supporters in the 1980s were known to have a lot of racist supporters, giving some awful abuse to say Paul Cannoville (their first black player).
I remember after the Battle of Stamford Bridge in 1988 reading in the local London papers a large group of Chelsea fans were convicted of attacks on Boro fans, their addresses were Addicombe (which then was mainly posh former council houses that had been bought). They generally had good jobs say say working at low levels in the City, but became a bit of Weekend Warriors, to sort of prove they were masculine and working class still. A bit like in the book/film the Football Factory where the main Chelsea hooligans worked during the week in a Florist suppliers.
West London has a lot of Chelsea fans too, but there is more competition, with Fulham, QPR and Brentford.
Nowadays Chelsea is just another plastic club to me, with fans supporting them because they are one of the big five and watching them on TV, but not going to games.