Corpus of Contemporary American English (COCA)

http://corpus.byu.edu/coca/

The Corpus of Contemporary American English (COCA) is the largest freely-available corpus of English, and the only large and balanced corpus of American English. It was created at Brigham Young University in 2008, and it is now used by tens of thousands of users every month (linguists, teachers, translators, and other researchers). COCA is also related to other large corpora that we have created or modified, including the British National Corpus (our architecture and interface), the 100 million word TIME Corpus (1920s-2000s), and the new 400 million word Corpus of Historical American English (COHA; 1810-2009).

The corpus contains more than 425 million words of text and is equally divided among spoken, fiction, popular magazines, newspapers, and academic texts. It includes 20 million words each year from 1990-2011 and the corpus is also updated once or twice a year (the most recent texts are from March 2011). Because of its design, it is perhaps the only corpus of English that is suitable for looking at current, ongoing changes in the language (see the 2011 article in Literary and Linguistic Computing).