If you own rental property in Maricopa County then, it is required to register those properties with Maricopa County. An owner who fails to file the required information may be fined $1,000 plus an additional $100 for each month the filing is delinquent.
You can download the registration form at
http://www.maricopa.gov/assessor/pdf/residentialrentalform.pdf
I hope this information was helpful for you and if you know of anyone who may benefit from this, please pass the information along.