As of 2015, the U.S. Secret Service is authorized to track cell phone service usage of American citizens. More broadly, the National Security Agency acquires a substantial quantity of domestic cell usage metadata through mass surveillance.
Many American law enforcement agencies perform targeted surveillance on domestic cell phones. These agencies typically use "Stingray" IMSI-catchers to determine the locations of targeted phones. These cell phone tracking tools are used extensively by the Baltimore Police Department.
The NSA collects some domestic cell phone usage data through incidental or non-deliberate collection through global mass surveillance operations. However, the NSA ceased bulk collection of domestic Verizon telephony metadata in June 2015.