Ida was born in Canton, Ohio, in 1847, the eldest daughter of a socially prominent and well-to-do family. James A. Saxton, a banker, was indulgent to his two daughters. He educated them well in local schools and a finishing school, and then sent them to Europe on the grand tour.

As a young woman, she worked in her father's bank. As a cashier she caught the attention of Maj. William McKinley, who had come to Canton in 1867 to establish a law practice, and they fell deeply in love. While he advanced in his profession, his young wife devoted her time to home and husband. A daughter, Katherine, was born on Christmas Day, 1871; a second daughter, Ida, was born in April 1873. Ida was seriously ill after the birth, and baby Ida died four months later. Katie succumbed to typhoid fever in August 1875, leaving the McKinleys childless. Phlebitis and epileptic seizures afflicted Mrs. McKinley throughout her adult life.

As congressman and then as governor of Ohio, William McKinley was never far from her side. He arranged their life to suit her convenience. She spent most of her waking hours in a small Victorian rocking chair that she had had since childhood; she sat doing fancy work and crocheting bedroom slippers while she waited for her husband, who indulged her every whim.

At the White House, Mrs. McKinley did not allow her health to hinder her role as first lady. She received guests at formal receptions seated in a blue velvet chair. She held a fragrant bouquet to suggest that she would not shake hands. Contrary to protocol, she was seated beside the president at state dinners and he, as always, kept close watch for signs of an impending seizure. If necessary, he would cover her face with a large handkerchief for a moment. Guests were discreet and newspapers silent on the subject of her "fainting spells." Only in recent years have the facts of her health been revealed.

When the president was shot by an assassin in September 1901, after his second inauguration, he thought primarily of her. He murmured to his secretary: "My wife—be careful, Cortelyou, how you tell her—oh, be careful." After his death she lived in Canton, cared for by her younger sister, visiting her husband’s grave almost daily. She died in 1907, and lies entombed beside the president and near their two little daughters in Canton’s McKinley Memorial Mausoleum.