[Kazz D'Avore]

silchas ruin mentions in MT that the forkrul assail had cities underground, but says something along the lines of that they didnt live their 'but only gathered.'

he also mentions that the FA thought that they had won their internal war for balance and so went out looking to create it in the outside world... by killing everyone they met

[Aptorian]

So yes... there were many of them. A "City" implies many.