When they first started tracking markets in 1994, there were about 3,500. AMS maintains a database of nationwide markets, so for those traveling out of California, you can check it out before you go: http://apps.ams.usda.gov/FarmersMarkets/
And for those of us living here in LA, according to the Los Angeles County Agricultural Commissioner/Weights and Measures there are over 100 certified farmers' markets in the County, meaning there's bound to be one near you. Check them out: http://acwm.co.la.ca.us/scripts/CertifiedFM.cfm
We also have some of the most diverse markets in the nation. We have the almost carnival-like atmosphere of the Sunday Hollywood Farmers' Market:And, the relaxing and beautiful coast alongside the Thursday, Redondo Beach Farmers' Market.