Not a club very well placed to attract fans due to constraints of geography and team performance.
Geographically, their catchment area only really extends as far as the city of Coventry itself and local parts of Warwickshire. So around 500,000 people then, maybe a bit less. However they are right next door to four Premiership clubs in the Birmingham conurbation, so it's rotten luck for them as locals would probably rather travel a few more miles to watch Villa than watch their local side. In terms of League performance, they've floundered ever since they were relegated from the Premiership a decade ago. They clearly still have floating fans who turn up when a big team comes to town (e.g. 28,000 attendance for their home game against Leeds) but obviously when you're less successful and playing less attractive opposition, you'll only get half that crowd turning up. I'm sure Leeds' away following made a big contribution to that figure too, nigh on 6,000 Leeds fans there that day.