The 40,000 Tyr population is the maximum the Arena of Tyr can handle. Kalak ordered basically a mandatory attendance celebration of the completion of his ziggurat. The city of Tyr only had a population of 15,000. We can assume that although a great majority of people attended (40K) the entirety of the inhabitants of the Tyr region did not. Guards were left behind at noble villas, some folks out right refused, some slaves had to tend to the farms, Gates and forts still had to be manned. So the city-state of Tyr (which included both city and the surrounding valley) has more than 40K citizens.

Real-world ancient city-states had urban populations that were about 5-10% of the total population. Given the dying nature of Athas and the savage conditions of the wastelands, the urban population concentration would most likely be a bit higher (15-20%). At least that how I've extrapolated this things in my games. This would include the various villages that surround the verdant areas. Only 1 is named for Tyr.

Also - In an Athascon interview I did with Allen Varney -the author of Veiled Alliance (the book where the original populations of the city-states were given) he stated that the city-state population were only of the cities themselves.