I know it's at least three. My dad grew up in Lutterworth and his dad (my late granddad) used to take him to matches in the sixties and seventies.
My dad then moved to Cambridgeshire in the early nineties for work reasons and brought me and my siblings up as Leicester supporters, my first memories of which involve having a poster of Steve Guppy on my bedroom wall.
At school I was surrounded by Manchester United, Liverpool and Arsenal fans, none of whom ever attended matches, obviously. There were also a fair amount of Ipswich fans, and those are the only people I interacted with who actually went to football matches like I did.
It's strange to think that when I was at primary school (mid nineties to early noughties) I was teased about supporting Leicester as if they were a "rubbish" team, and this was in the O'Neill era to start with. Nowadays, as an adult, few people would mock someone about supporting a side that consistently finished in mid table in the Premier League.