Population growth and foreign-born population. Between 1970 and 1990, McKinney experienced moderate population growth, from 15,193 in the 1970 census, to 21,283 in the 1990 census. Since then, McKinney's rate of increase has been much more dramatic. In the 2000 census, McKinney had grown to 54,369 and to 131,117 in the 2010 census.