In a blog post, Richard Salgado, Google's director of law enforcement and information security, said the company worked with government officials to provide greater insight into the process.
Salgado said the company had to provide numerical ranges instead of exact figures to address the concerns raised by the FBI, the Justice Department and other agencies that exact numbers could reveal information about sensitive investigations.
Michelle Richardson, legislative counsel for the American Civil Liberties Union, said the number of National Security Letters was not surprising but the fact that Google released them at all was "unprecedented."
"It's the first instance I'm aware of where a corporation has worked with DOJ to release these numbers," Richardson said.
She encouraged other companies that receive the requests, such as telephone companies, Internet providers and other email companies, to release their own figures.
The Justice Department's Inspector General revealed in 2008 that the FBI had issued between 39,000 and 57,000 National Security Letters each year between 2003 and 2006.