You can do the math:
Billie Jo was played by 3 different actresses:
Jeannine Riley b: Oct 1, 40
Gunilla Hutton b: Mar 15, 44 (Was also on Hee Haw, as I recall)
Meredith McRae b: Mar 30, 44 (Has in acted numerous shows)
Bobby Jo was played by two different actresses:
Pat Woodell b: July 12, 44
Lori Saunders b: Oct 4, 44
Betty Jo was portrayed by only one actress throughout the 222 episodes:
Linda Kay Henning b: Sept 16, 44
