Adam's phone number shows up on Diana's phone as (206) 555-0144. The 206 area code covers areas in and around Seattle, WA.
The paper on the wall at Jake's grandfather's house lists the birthdays of the members of The Circle as follows:
Jake Armstrong: October 8, 1992
Nick Armstrong: August 29, 1994
Adam Conant: January 28, 1995
Faye Chamberlain: February 25, 1995
Cassie Blake: March 28, 1995
Diana Meade: August 18, 1995
Melissa Glaser: May 6, 1995
The license plate on Cassie's SUV is Washington plate #679 M1A.
The license plate on Dawn Chamberlain's car is Washington plate #319 M2P. The plate on Charles Meade's car is Washington plate #535 OTN.
When Diana and Adam break into Zachary Larson's student records, they see his disciplinary history under the heading "Vice Principle's Notes," which should read "Vice Principal's Notes."