This is an old figure, but according to the Census of Agriculture there
were 128,170 women farm operators in the US in 1978 (5% of all farmers
were women). This number only represents the women who are main or sole
operators of their farms. Women farmers working as partners in farming
operations are undercounted because usually the husband is considered the
main operator. (reference: Kalbacher, J. Women farm operators: A
statistical profile. In Women's roles on North American farms. Proceedings
of a seminar. July 1982. Racine, Wisconsin)