Killeen is a city in Bell County, Texas, United States. According to the 2010 census, its population was 127,921, making it the 21st-most populous city in Texas. It is the principal city of the Killeen–Temple–Fort Hood Metropolitan Statistical Area.Killeen is directly adjacent to the main cantonment of Fort Hood. Its economy depends on the activities of the post, and the soldiers and their families stationed there. It is known as a military “boom town” because of its rapid growth and high influx of soldiers.