From USA Today:

The report by a Pentagon inspector general, made public under a Freedom of Information Act request, said spy drones on non-military missions have occurred fewer than 20 times between 2006 and 2015 and always in compliance with existing law.

The inspector general analysis was completed March 20, 2015, but not released publicly until last Friday.

It said that with advancements in drone technology along with widespread military use overseas, the Pentagon established interim guidance in 2006 governing when and whether the unmanned aircraft could be used domestically. The interim policy allowed spy drones to be used for homeland defense purposes in the U.S. and to assist civil authorities.