USA AT LARGE: Here is a good starting place for the nation at large.
NASHVILLE / MIDDLE TN: Tiny Houses added to a property with an existing structure are considered DADUs (Detached Accessory Dwelling Units). In short, you can put a tiny house on any properties that are zoned R80-R6, RM2-RM20-A, RM40-RM100A, OR20-OR40A and ORI and ORI-A; AND in an historic overlay are eligible. HERE and HERE are links to pages with DADU information and zoning codes for Nashville. HERE is a Metro Nashville map that will show the zoning for your property. Just punch in your address and refer to the above lists to know if your property is eligible.‍