The denomination of Origin includes the whole State of Jalisco(that is where the town of Tequila is located) and parts of the following states: Nayarit, Guanajuato, Michoacán and Tamaulipas. Most of the producers are located in Jalisco and that is where the majority of the tequila is produced. This is why you will find a lot more references to Jalisco vs. the other states when someone is talking about tequila.
Denominations and appellations can set other kinds of qualifying criterias for ingredients, special processes and other limitations to further control the quality.
In the world of tequila, the quality control applies to 3 major elements: