Takes place ten years after "The First Purge", between the first/second & third movies.
Several people mention the "Sandin system", James Sandin is the protagonist in the first Purge film, and made his fortune of selling the Sandin security system.
The Betancourts are named after co-executive producer Mick Betancourt.
Denzel Whitaker was 29 as he was playing an 18 year old college student.
The Kantrow facility is named after producer Alissa M. Kantrow.