In 1938, while on an expedition to Oaxaca, Mexico, Mexía became ill. Forced to abort the trip and return to the United States, she was subsequently diagnosed with lung cancer and died a month later at the age of 68. William E. Colby, then secretary of the Sierra Club, wrote, "All who knew Ynés Mexía could not fail to be impressed by her friendly unassuming spirit, and by that rare courage which enabled her to travel, much of the time alone, in lands where few would dare to follow."