AT&T is one of several carriers with a 5G network in the US and was the first to launch mobile 5G services in select cities on December 21, 2018.
AT&T's 5G+ service (the mmWave type) is live in more than 50 cities, including:
AT&T's low-band 5G network is available in more than 22,000 cities. They also use mid-band spectrum to provide a combination of high speeds and wide coverage.
As of January 2024, this is AT&T's 5G coverage map for the continental US and southern Canada: