74.81%. 1  Graph: Population by Age and Race - Mckinney, Texas. 2  Graph: Population by Age and Race, 2000 Census - Mckinney, Texas. 3  Graph: Change in Population between 2000 and 2010, by Age and Race - Mckinney, Texas. 4  Graph: Population by Age and Hispanic or Latino Origin, 2010 Census - Mckinney, Texas.