Milliken campaigned vigorously for abortion rights and the ill-fated Equal Rights Amendment, which stated equality of rights "shall not be denied or abridged by the United States or by any state on account of sex."
She drew the wrath of the outdoor advertising industry shortly after her husband, Republican William Milliken, became governor in 1969, when she criticized highway billboards as unsightly clutter. And at her urging, her husband hiked the Pigeon River State Forest while governor and later decided to limit oil and gas development in the scenic forest.
Milliken died on Friday morning at her family's home in Traverse City, her son, William "Bill" Milliken Jr., said. She had been diagnosed with ovarian cancer, he said, and was receiving hospice care. She was 89.
It was the couple's daughter, Elaine, a lawyer and feminist, who died of cancer in 1993, who influenced her mother to take a stand for women's equality. Helen Milliken served as national co-chair of ERAmerica and was a delegate to the International Women's Year conference in Houston. Her other board memberships included the Women's Resource Center and the Michigan Land Use Institute.
Even into her 80s, she remained active in community affairs and as an environmentalist. Milliken helped organize a foreign policy lecture series at Northwest Michigan College and took a course on the life of Mozart.
Milliken co-founded ArtrainUSA, an art museum housed in rail cars that visited more than 850 communities across the U.S. since 1971.
She told The Associated Press in 2006 about her concerns that many younger women were shying away from political activism and the "feminist" label.
"They don't know their history," she said at the time. "Young women take so much for granted now."
Feminism, she said, had "been redefined and misinterpreted" by conservatives as wild-eyed radicalism.
"Nobody ever saw anybody burn a bra; they're too expensive," she said. "But the myth has survived. There have been excesses, but the goal has always remained the same: equal opportunity for women."
Gov. Rick Snyder in a statement praised Milliken for her "countless" contributions to the state.
"As a champion of women's issues, patron of the arts and dedicated environmentalist, Mrs. Milliken lent her strong voice to causes that enrich our state to this day," Snyder said. "Long after Governor Bill Milliken left office, she remained a driving force for the betterment of Michigan, because she loved this state and believed in its future.
"Mrs. Milliken set the standard for the next generation of first ladies."
The former Helen Wallbank, daughter of a Denver-area attorney, earned a bachelor's degree from Smith College in 1945, and met William Grawn Milliken as he underwent military training in Colorado during World War II.
After marrying, they settled in his Michigan hometown of Traverse City, which also was home to the family-owned Milliken Department Store.
William Milliken was elected to the state Senate in 1960, following in the footsteps of his father and grandfather, both Republican state senators. Shortly afterward, Milliken and other moderates rebelled against the right-wing leadership, issuing a manifesto with progressive stands on issues such as taxes and civil rights.
Elected lieutenant governor in 1964 and 1968, Milliken succeeded fellow Republican George Romney as governor in January 1969 when Romney joined President Richard Nixon's Cabinet. Milliken won the election that fall and was re-elected twice, but decided not to seek a fourth term in 1982. He retired from politics unbeaten at age 59.
His wife, however, wasn't done with politics.
Helen Milliken continued to be a sought-after political commodity long after her husband's retirement. In 1994, she was even asked to be the running mate of Democratic gubernatorial candidate Howard Wolpe as he sought to boost his underdog campaign against Republican Gov. John Engler.
She declined, later telling the AP "it just didn't seem like the right move to make at the time."
Current U.S. Sen. Debbie Stabenow ended up as Wolpe's running mate in that ill-fated race against Engler.
On Friday, she remembered Milliken as "a role model and a dear friend."
"I will miss her greatly. Her extraordinary and courageous leadership came at a time when we needed strong voices for women, and her efforts to protect women's health, the Great Lakes and our Michigan outdoors will leave a legacy that will be felt for many generations to come," Stabenow said.
Longtime U.S. Rep. Sander Levin said Milliken was a leader, "with strong views of her own, a keen intellect and a deep and abiding commitment to so many causes she was passionate about."
"Helen Milliken was a vigorous, highly valued partner with her husband, Governor Milliken, in a team that has represented the very best in public service," Levin said.
Milliken is survived by her husband and her son, William Jr., of Ann Arbor, and her sister, Elaine Jackson of Denver. The family said a memorial service will be held at a later date. Reynolds-Jonkhoff Funeral Home in Traverse City is handling arrangements.