Was it a duchy? A county? Or even smaller? Was it ever mentioned in the suttas? Are there books or sources regarding this?
You can check out this map to get some idea.
Sākya is a bit below the word ‘Nepal’ on the map and as you can see it is located in Kosala. It was a vassal state of Kosala.
Here is another collection of maps that might be helpful:
I read that sakya was a republic? Was Kosala also a republic?
Kosala was a kingdom . Though the Sakyans were very proud which led to their downfall when the offered a slave girl to the ķing. When the king found out he attaked the Sakyans a d dextroyed them.