SAN FRANCISCO — Cellphone carriers last year answered at least 1.1 million requests from law enforcement agencies seeking information on caller locations, text messages and other data for use in investigations, according to reports from the carriers.

Most of the requests were for information from a specific customer account. But law enforcement agencies also received information from 9,000 so-called tower dumps, in which the agencies were granted access to data from all the phones that connected to a cell site during a specified period of time.

The cellphone carriers’ reports, which came in response to a congressional inquiry, underscored the law enforcement agencies’ strong reliance on wireless phone records. The carriers are shown to turn over records thousands of times a day in response to police emergencies, subpoenas and other requests.

Senator Edward J. Markey, a Massachusetts Democrat, requested the reports from seven carriers, including AT&T, Verizon Wireless, Sprint and T-Mobile US. Mr. Markey conducted a similar audit last year as a member of the House, seeking information from carriers about law enforcement requests for 2011.