On July 22, 2016, it was announced that Janina Gavankar had joined the cast in a recurring role as Diana, Ichabod's new partner. Described as a single mom, and a former military officer who serves as a special agent for Homeland Security. Also cast in a recurring role is former MasterChef Junior contestant Oona Yaffe, who will play Diana's ten-year old daughter Molly Thomas. Rachel Melvin joined the cast as Alex Norwood, her character has been described as a self taught engineering prodigy who works alongside Jake Wells (Jerry MacKinnon) in the supernatural archives in Washington D.C. Jeremy Davies joined the cast in a recurring role as villain Malcolm Dreyfuss, a billionaire tech mogul who aspires to conquer other worlds, described as a dark mirror to Ichabod Crane. James Kyson joined the cast in a role yet to be announced. During the show's New York Comic Con panel on October 9, 2016, it was revealed that John Noble will be returning this season as Henry Parrish / Jeremy Crane; however, it was not revealed on whether he will be recurring or guest-starring in this season. On November 1, 2016, it was announced that Kamar de los Reyes will be starring in a recurring role this season. Robbie Kay was cast in the role of Logan MacDonald on November 23, 2016.
Due to the show changing its setting to Washington, D.C., it was announced that stars Lance Gross who played FBI Agent Daniel Reynolds, and Jessica Camacho who played FBI Agent Sophie Foster in Season 3 would not be returning. However, it was also teased that Camacho might make a few guest appearances in Season 4.
Production on the fourth season began on August 15, 2016 in Atlanta, Georgia. On October 11, 2016, it was reported that filming was taking place in the city of Lawrenceville, Georgia; pictures from the set of the show were also shared on social media.