Population of Morrill County Last official estimated population of Morrill County was 5,040 (year 2014) [1]. This was 0.002% of total US population and 0.3% of total Nebraska state population. Area of Morrill County is 1,429.9 miÂ² (=3703.3 kmÂ²), in this year population density was 3.52 p/miÂ².