McGregor, Texas. McGregor is a city in McLennan and Coryell counties in the U.S. state of Texas. The population was 4,987 at the 2010 census. McGregor lies in two counties, as well as two metropolitan areas. The McLennan County portion of the city is part of the Waco Metropolitan Statistical Area, while the small portion that lies in Coryell County is part of the Killeen–Temple–Fort Hood Metropolitan Statistical Area.