It's both shocking and unsurprising that the first Federally endorsed Women's History celebration didn't occur until 1980 and was only a week long. Here's a brief history from the National Women’s History Museum: “The Education Task Force of the Sonoma County (California) Commission on the Status of Women planned and executed a “Women’s History Week” celebration in 1978. The organizers selected the week of March 8 to correspond with International Women’s Day. The movement spread across the country as other communities initiated their own Women’s History Week celebrations the following year.
In 1980, a consortium of women’s groups and historians—led by the National Women’s History Project (now the National Women's History Alliance)—successfully lobbied for national recognition. In February 1980, President Jimmy Carter issued the first Presidential Proclamation declaring the Week of March 8th 1980 as National Women’s History Week.”
Again, fueled by the action of women's groups, it took until March of 1987 for Women’s History Month to be signed into law. Unfortunately, it was only acknowledged by a few states. It wasn't until 1995(!) that each POTUS annually proclaimed the entire month of March as Women’s History Month.