The HATNet Project telescopes HAT-7, located at the Smithsonian Astrophysical Observatory's Fred Lawrence Whipple Observatory in Arizona, and HAT-8, installed on the rooftop of Smithsonian Astrophysical Observatory's Submillimeter Array building atop Mauna Kea, Hawaii, observed 33,000 stars in HATNet field G154, on nearly every night from late May to early August 2004. The light curves resulting from the 5140 exposures obtained were searched for transit signals and a very significant periodic drop in brightness was detected in the star GSC 03547-01402 (HAT-P-7), with a depth of approximately 7.0 millimagnitude, a period of 2.2047 days, and a duration of 4.1 hours.