Oh well, since I unshelved some books:
Darkon: Population 117,300, halflings 14%
Necropolis: Population 26,800, halflings 17% (but undead)
Falkovnia: Population 64,300, halflings 2% (mostly slaves)
Hazlan: Population 26,100, halflings 4% (mostly slaves)
Richemulot: Population 45,330, halflings 5% (good chance them being wererats)
Missing information from gazetteer V if anyone wants to fill in. The countries which are not mentioned may host halflings in the 1-2% in which they say "Others" but may be a very very sporadic, incidental and non-influential number.