Whedon is the creator of the iconic TV shows "Buffy the Vampire Slayer," "Angel" and "Firefly." Whedon co-wrote "Cabin" with "Cloverfield" scribe Drew Goddard, who is also directing "Cabin."
Jenkins, a former cast member of TV's "Six Feet Under," starred in "The Visitor," "Burn After Reading" and "Step Brothers" last year.
Whitford is best known for his work on the TV dramas "The West Wing" and "Studio 60 on the Sunset Strip."
"It's really just your basic typecasting: When you need two actors to run through the woods in low-cut nighties, you immediately think of Richard Jenkins and Bradley Whitford," Goddard joked to The Hollywood Reporter.
"They're the first proof that, though 'The Cabin in the Woods' is a classic horror film, it isn't one you've seen before," Whedon added.
The entertainment industry trade newspaper said few details about the film's plot are known, but rumor has it Jenkins and Whitford will play white-collar co-workers with a mysterious connection to the titular cabin.
The movie is slated to begin shooting this spring for an anticipated Feb. 5, 2010, release date.