 The population density was 41.2 people per square mile (15.9/km²).The racial makeup of Onyx was 406 (85.5%) White, 4 (0.8%) African American, 9 (1.9%) Native American, 0 (0.0%) Asian, 0 (0.0%) Pacific Islander, 16 (3.4%) from other races, and 40 (8.4%) from two or more races.Hispanic or Latino of any race were 30 people (6.3%).