Ryan was born Jeri Lynn Zimmermann in Munich, West Germany, the daughter of Gerhard Florian "Jerry" Zimmermann, a master sergeant in the United States Army, and his wife Sharon, a social worker. She has one older brother, Mark. As a military brat, Ryan grew up on army bases in Kansas, Maryland, Hawaii, Georgia, and Texas. When she was eleven, her father retired from the Army and the family settled in Paducah, Kentucky. She graduated from high school in 1986 (as a National Merit Scholar), and then attended Northwestern University, where she was a member of the Alpha Phi sorority.

In 1989, Ryan was chosen Miss Illinois. She was the third runner-up in the 1990 Miss America Pageant, winning the preliminary swimsuit competition. She graduated from Northwestern in 1990 with a Bachelor of Arts degree in Theatre.