Terry S. Kogan - Laws in the U.S. did not even address the issue of separating public restrooms by sex until the end of the 19th century, when Massachusetts became the first state to enact such a statute. By 1920, over 40 states had adopted similar legislation requiring that public restrooms be separated by sex.
These laws were rooted in the so-called “separate spheres ideology” of the early-19th century – the idea that, in order to protect the virtue of women, they needed to stay in the home to take care of the children and household chores.
During America’s early history, the household was the center of economic production, the place where goods were made and sold. That role of the home in the American economy changed at the end of the 18th century during the Industrial Revolution. As manufacturing became centralized in factories, men left for these new workplaces, while women remained in the home.
Soon, an ideological divide between public and private space arose. The workplace and the public realm came to be considered the proper domain of men; the private realm of the home belonged to women. This divide lies at the heart of the separate spheres ideology.
... Midcentury regulators also adopted architectural solutions to “protect” women who ventured outside the home.
Architects and other planners began to cordon off various public spaces for the exclusive use of women. For example, a separate ladies' reading room – with furnishings that resembled those of a private home – became an accepted part of American public library design. And in the 1840s, American railroads began designating a “ladies' car” for the exclusive use of women and their male escorts. By the end of the 19th century, women-only parlor spaces had been created in other establishments, including photography studios, hotels, banks and department stores. Sex-separated restrooms: putting women in their place?
It was in this spirit that legislators enacted the first laws requiring that factory restrooms be separated by sex.