Not 100% sure if all objects in the loaded region are loaded (Npcs for example get loaded in a 16x16 area), but judging by your estimation, it should be 104x104, which is the size of one region.
For GameObjects it will be your loaded region, which as @Savior said, is 104x104. It's important to not that this area is not necessarily centred on your character, so a GameObject 20 coordinates away from you may not be loaded, as it's in another region.
