Population of McKinney, TX. Last official estimated population of McKinney city (Collin County**, Texas state) was 156,767 (year 2014)[1]. This was 0.049% of total US population and 0.57% of total Texas state population. Area of McKinney city is 62.8 miÂ² (=162.8 kmÂ²) [6], in this year population density was 2,494.38 p/miÂ². If population growth rate would be same as in period 2010-2014 (+4.57%/yr), McKinney city population in 2018 would be 187,435*.