What are the requirements to join police academy?

It varies from department to department. I suggest going on the internet and searching a specific department's requirements.
But as a general rule it would be something like.
1.) Must be 20.5 years old at time of application.
2.) United states citizenship.
3.) Valid drivers license issued by the state you are applying in.
4.) No prior drug use within a certain time frame (Or over a certain amount of times)
5.) No prior felonies (Obviously)
6.) Good driving record (What constitutes a good driving record may vary department to department)
7.) Tattoos must not be visible on the forearms, hands, or wrists. (Once again, varies from department to department)
8.) Good financial and employment record.