Contrary to the windmills in for example The Netherlands in early 17th century, the Spanish towermills had a relatively low power output due to their small size, inefficient sail design and use of materials. This meant that even for a small village, a multitude of windmills was necessary to provide the required meal. In Portugal one miller often tended to a group of windmills, while in north-western Europe one or more millers were busy with one mill.

Although the windmills have fallen in disuse the past 100 years, you can still see the hilltops on the Iberian Peninsula dotted with rows of windmill ruins.

A group of 30 to 40 windmills may be a bit much (although I do not know the size of the town or it's geography), but a number of separate groups consisting of 10 to 20 surrounding a city were not uncommon.

Hope this helps, if you have further questions or want some deeper inside knowledge you can always ask. I'm a Dutch miller myself and have worked with a variety of windmills.