That's about double the area of Spain, so not too large. Especially considering much of it is arid and/or mountaineous, which limit population size. The cities shown on my map aren't the only ones that exist, but are the only ones that are proper city-states with representation in the league. All other towns would be smaller and non-independent, being under political domination of one of the big city-states.

Inhabitants should be entirely or almost entirely humans of Trinagonese ethnos. Any natives that may have dwelled on the island at the time the Trinagonese migrated there would have been expelled, absorbed, or reduced to extinction over the centuries that followed.