| Statistic | Millbrook | Illinois | National |
| Population | 357 | 12,671,821 | 328,239,523 |
| Population density (sq mi) | 193 | 228 | 91 |
| Median age | 41.5 | 37.4 | 37.7 |
| Male/Female ratio | 0.8:1 | 1.0:1 | 1.0:1 |
| Married (15yrs & older) | 67% | 55% | 55% |
| Families w/ Kids under 18 | 47% | 44% | 43% |
| Speak English | 99% | 77% | 79% |
| Speak Spanish | 1% | 13% | 13% |
| Race | Millbrook | Illinois | National |
| White | 99.16% | 72.14% | 73.35% |
| Black | 0.00% | 14.30% | 12.63% |
| Asian | 0.00% | 5.10% | 5.22% |
| American Indian | 0.00% | 0.23% | 0.82% |
| Native Hawaiian | 0.00% | 0.03% | 0.18% |
| Mixed race | 0.84% | 2.34% | 3.06% |
| Other race | 0.00% | 5.86% | 4.75% |
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