Directed by Jonathan Silverstein, performances are scheduled for July 10-Aug. 2 at the Pennsylvania venue.
Dullea and Dillon portray the long-married couple Norman and Ethel Thayer as they spend the summer on their lakeside cottage in Maine.
The production also has scenic design by Steven C. Kemp; costume design by Jennifer Paar; lighting design by Gina Scherr; and original music and sound design by Obadiah Eaves.
Tickets start at $29 and can be purchased by calling (215) 862-2121 or online at buckscountyplayhouse.org.
The Playhouse will also present The 25th Annual Putnam County Spelling Bee, beginning Aug. 14, followed by It's a Wonderful Life: A Live Radio Play this winter.