Hi Renee, you will need a permit to convert a garage. Here is the link to the Town of North Hempstead: http://www.northhempstead.com/ you will be able to find helpful information there about how to go about the conversion process. I wish you the best of luck!
In all areas I am aware of the answer is YES. Anytime you convert non living (conditioned) space to a living area, you need a permit...as a part of the process, the capacity of the a/c will be reviewed along with septic (if applicable)