Factual error: In several different episodes characters are escaping on foot to Canada, as evidenced by Ontario license plates. But the show is set in New England, and the only way to get to Ontario through the Eastern United States is by crossing a major body of water: The St. Lawrence River, Lake Ontario, The Niagara River, or Lake Erie. You can't walk there.
Episode #2.1 - S2-E1
Factual error: Season 2 is set in 1979. Bill Tench and his wife are leaving the church and going to their car. Behind their car is parked a 1981 Chevrolet Celebrity.
Factual error: DI Renton is a Metropolitan Police officer 'parachuted' into Kent to solve a big case. This hasn't happened for many decades. Local police forces investigate their own crimes without help from the Met.
Factual error: When Detective Inspector Sara Lunt's photograph in uniform is shown on the TV news she is wearing a double row of silver lace below her hat badge. Only chief constables wear this insignia, well above the rank of inspector.
Episode #4.9 - S4-E9
Factual error: Renate escapes from the prison in a Morris Ten Four, with the badge visible on the bonnet. However, this designation was not introduced until 1935 and the episode is set in 1931.
Factual error: The judge rules in favor of Wendy's father despite not hearing any testimony from his primary witness, who fails to appear. The judge states on the record that he is making this ruling because of the Byrdes' "reputation" rather than any testimony. This is absolutely ludicrous. A judge is not allowed to make a ruling on a child custody case based entirely on his opinion of the litigants, which he doesn't even elaborate upon, rather than any evidence or testimony before him.
Factual error: The provincial police is always described as the Ontario Police Department (OPD) instead of the correct Ontario Provincial Police (OPP).