The Bureau of Labor Statistics is the "principal Federal agency responsible for measuring labor market activity, working conditions, and price changes in the economy." For our purposes, we're most interested in data on the composition of the workforce.
Note that the online data only goes back to the early 2000s for detailed breakdowns of occupations by sex.
Fortunately, the BLS has created a section of its website devoted specifically to women's issues. I've provided a link to that information below, as well as a few others link that might be useful if you need more detailed info.
Much of the data from earlier than 2000 has been compiled in the various Handbooks on Women Workers, published by the Women's Bureau of the Department of Labor on a periodic basis from the 1930s into the 1990s.
We have print copies of several of these publications: 1954, 1956, 1958, 1960, 1962, 1965, 1969, 1975, 1983, 1993. They are located at call number L 36.103X in the government documents collection on the first floor (please ask for help finding these -- gov doc call numbers are notoriously hard to use).
Digitized versions of these publications are now also available (from the HathiTrust, a consortium of large research libraries) for the following years:
The Bureau of Labor Statistics publication, Employment and Earnings, has data on the number of women in a variety of professions. We have this publication back to 1985 in print (at call number L 2.41/2 in the government documents collection), and then back to 1975 on microfilm. This publication has also been digitized by the HathiTrust and made available online. Because there are so many issues of this publication (it was printed monthly), I am not providing individual links here to digitized copies. To find digitized versions of Employment and Earnings, go to the HathiTrust link below, and search "Employment and Earnings," as a TITLE search.