For those (of all races) making less than $30K, 401k participation rate is around 50% (50% for AA and Hispanic, 54 for Asians and 56% for whites... those participation rates increase as income increases (for all races)
See page 7 (and 8) of this report:
https://www.arielinvestments.com/images/stories/PDF/arielhewittstudy_finalweb_7.3.pdf