“Thought is free.”

Alabama Republican Assemblies Luncheon, April 29, 2000. http://renewamerica.us/archives/speeches/00_04_29alral.htm.
2000

United States v. Schwimmer, 279 U.S. 644 (1929) (Holmes, J., dissenting).
1920s

"For the Defense Written for the Associated Press, for use in my obituary" (20 November 1940)
1940s–present
Context: Having lived all my life in a country swarming with messiahs, I have been mistaken, perhaps quite naturally, for one myself, especially by the others. It would be hard to imagine anything more preposterous. I am, in fact, the complete anti-Messiah, and detest converts almost as much as I detest missionaries. My writings, such as they are, have had only one purpose: to attain for H. L. Mencken that feeling of tension relieved and function achieved which a cow enjoys on giving milk. Further than that, I have had no interest in the matter whatsoever. It has never given me any satisfaction to encounter one who said my notions had pleased him. My preference has always been for people with notions of their own. I have believed all my life in free thought and free speech—up to and including the utmost limits of the endurable.

Talking about his daughter, Sarah Lee learning Alice's Restaurant Massacre. (Live in Sydney)

Unconstitutional Legislation Threatens Freedoms, May 7, 2007 freerepublic.com http://www.freerepublic.com/focus/f-news/1830822/posts
2000s, 2006-2009

Source: 1920s, Sceptical Essays (1928), Ch. 12: Free Thought and Official Propaganda http://books.google.com/books?id=9tQsg5ITfHsC&q="It+is+clear+that+thought+is+not+free+if+the+profession+of+certain+opinions+makes+it+impossible+to+earn+a+living"&pg=PA126#v=onepage

Source: Gargantua and Pantagruel (1532–1564), Fifth Book (1564), Chapter 15.