Ada Hayden (14 August 1884 – 12 August 1950) was an American botanist, educator, and preservationist.
She was the curator of the Iowa State University Herbarium, which was renamed the Ada Hayden Herbarium (ISC) in her honour in 1988.
During her career, she added more than 40,000 specimens to the herbarium.
Her studies and conservation work were particularly important in ensuring the preservation of the tallgrass prairie.The Hayden Prairie State Preserve, the first area dedicated as a preserve under Iowa's State Preserves Act of 1965, is named in her honor.
Also named in her honor is the Ada Hayden Heritage Park in Ames, Iowa.