Sunnyvale is a town in Dallas County, Texas, United States. It is the easternmost city completely within Dallas County. The population was 7,893 in 2020. The area now occupied by Sunnyvale was inhabited by various Native American tribes in the years before the European conquest of the Americas. It came under the rule of Spain in the 18th century, …Sunnyvale is a town in Dallas County, Texas, United States. It is the easternmost city completely within Dallas County. The population was 7,893 in 2020. The area now occupied by Sunnyvale was inhabited by various Native American tribes in the years before the European conquest of the Americas. It came under the rule of Spain in the 18th century, very close to the boundary of Spanish and French territory. During this time, the area was relatively underdeveloped. However, some settlers migrated to Texas and would eventually settle in Sunnyvale.