Each parcel in every county is zoned for a specific number of living units (most often defined by the presence of a kitchen). If you wish to exceed the allowed number, you will need a variance which is costly, time consuming and likely to be denied.
Aside from the Planning Department, you will need to address the concerns of the Building Department (code compliance and build certification), as well as the Public Works Department (roads and drainage) and Environmental Health (wells, water and septic).
In order to place additional living units on your property, you will need to submit design drawings for your plans (often required to be prepared by a licensed design professional) to locate the additional units (Tiny Houses) to each of these four departments and get approvals.