The concept was created in the 1960's in Japan, Germany, and Switzerland in response to growing concerns over food safety and the urbanization of agricultural land. It was introduced on two farms in the Northeastern United States in the 1980's by two European farmers. By 2007 there were 13,000 CSA Farms in North America per the U.S. Department of Agriculture of which over 90% were in the US alone. Their growth and popularity seems to correlate with the rise in consumers wanting to know where their food comes from and how it is raised.
Here are a couple of links where you can learn more about CSA.