Where can I find information about number of current doggie daycare customers?

Answer 1

Sit outside of one such daycare in your area and count how many people come and go from their store during the day!

Answer 2

I don';t think that sort of market research has been done that's broken out by state, but I could be wrong.

Have you checked how many doggie daycares are in your city, then multiplied each by a customer count of 100 people (figure off and on useage, not steady customers). It could get you a local size of some sort.