Juan Diego Botto, who plays "Javier", is the real life brother of María Botto, who plays his sister "Ava" on the show.
Javier's Argentinian background was added to the character once the creators got to know Juan Diego Botto and learned about his Argentinian background.
Juan Diego Botto (Javier) dislocated his right shoulder on the 3rd day of the shoot and so in many of the car sequences Michelle Dockery (Letty) had to manually shift the gear lever from the front passenger's seat just out of view of the camera.
The selection of wigs that Letty wears throughout the series each had its own name on set: "Brittany" (long blonde), "Annie" (red), "Veronica" (short blonde) and "Katja" (short black bob).
The print in the probation officer's office is a replica of Wanderer Above the Sea of Fog, by German artist Caspar David Friedrich. The circa 1818 oil painting, also known as Wanderer Above the Mist or Mountaineer in a Misty Landscape, is housed in the Kunsthalle Hamburg, an art museum in Hamburg, Germany.