Population of Gridley, IL. Last official estimated population of Gridley village (McLean County**, Illinois state) was 1,448 (year 2014) [1]. This was 0% of total US population and 0.01% of total Illinois state population. Area of Gridley village is 1.2 miÂ² (=3.2 kmÂ²) [6], in this year population density was 1,173.42 p/miÂ². If population growth rate would be same as in period 2010-2014 (+0.28%/yr), Gridley village population in 2018 would be 1,464*.