Population of Payette County. Last official estimated population of Payette County was 22,638 (year 2014)[1]. This was 0.007% of total US population and 1.4% of total Idaho state population. Area of Payette County is 410.3 mi² (=1062.6 km²), in this year population density was 55.18 p/mi². If population growth rate would be same as in period 2010-2014 (+0.02%/yr), Payette County population in 2017 would be 22,649 .