Red Oak is a city in Ellis County, Texas, United States. It is part of the Dallas–Fort Worth metroplex. The population was 10,769 at the 201…Red Oak is a city in Ellis County, Texas, United States. It is part of the Dallas–Fort Worth metroplex. The population was 10,769 at the 2010 census, up from 4,301 at the 2000 census. The North Central Texas Council of Governments projects that number to grow to 63,329 by the year 2030, as it is on the verge of explosive suburban growth.