Mary Terstegge Meagher Plant (born October 27, 1964) is an American former competition swimmer, Olympic champion, and world record-holder.

At the 1979 Pan American Games in San Juan, Puerto Rico, she set her first world record—at the age of 14—in the 200-meter butterfly.

"Every athlete I've ever known had some form of weakness, be it in terms of motivation, technique or physical attributes, but Mary was the exception.

"[4] She graduated from the Sacred Heart Academy high school in Louisville, Kentucky, alongside her sister, future U.S. Representative Anne Northup.

She received the Honda Sports Award for Swimming and Diving twice, recognizing her as the outstanding college female swimmer of the year in 1984–85 and again in 1986–87.

Returning to compete at the 1988 Summer Olympics in Seoul, South Korea, Meagher won a bronze medal in the 200-meter butterfly.