Grayson County is a county in the U.S. state of Texas. As of the 2020 census, its population was 135,543. The county seat is Sherman. The county was founded in 1846 and is named after Peter Wagener Grayson, an attorney general of the Republic of Texas. Grayson County is included in the Sherman-Denison metropolitan statistical area, which is also included in the Dallas-Fort Worth-Arlington, combined statistical area. Located on the state's border with Oklahoma, it is part of the Texoma region, with proximity to Lake Texoma and the Red River.