How far from a volunteer fire department in order to volunteer?

Every department has their own rules on membership. I have been in 5 different departments. One required you to live in the boundaries of the department. My current one has a 2.5 mile radius around one of our firehouses. The rest didn't seem to care, because they had people doing shifts in addition to responding from home.
You need to look on their website or go down to the firehouse and ask.