Wilson has been cast in the important role of farm owner Hershel Greene, who allows the group of survivors to live with him for a short time, while Cohan will portray his young daughter Maggie.
"He is the patriarch of the family," The Walking Dead executive producer Gale Anne Hurd explained to TV Guide "He's a veterinarian with a great sense of humanity and a very unique take on the walkers [zombies]."
Hurd teased that Hershel's storyline would take a tragic turn when several members of his family are killed.
"She's in her 20s and is a survivor who ends up as a romantic interest for Glenn [played by Steven Yuen]," Hurd added, regarding Cohan's character. "Steven's very excited!"
Wilson is best known for portraying a killer in the 1967 thriller Cold Blood, while Cohan starred as the ancient vampire Rose on several episodes of The Vampire Diaries earlier this year.
Earlier this week Pruitt Taylor Vince joined the show's cast in a recurring role as Hershel's farmhand Otis.
Series creator Frank Darabont recently teased that the new season would focus primarily on the growing conflict between main characters Rick and Shane.
The Walking Dead returns for its second season on AMC in the US and on FX in the UK this October.
Watch a behind-the-scenes video of the The Walking Dead below: