Confusion around health insurance reforms persist. The purpose of this study was to assess demographic differences in Affordable Care Act (ACA) and health insurance knowledge in a multi-ethnic urban sample. Data came from 243 adults from racial/ethnic communities. Participants were asked about elements of health insurance and the ACA. Generalized linear and logistic regression models were used to examine relationships between demographic predictors and knowledge domains. Female gender (p < 0.05) and Latino/Hispanic race/ethnicity (p < 0.001) were most predictive of lower eligibility knowledge, while non-citizen with residency status (p < 0.001) and other/not declared residency status (p < 0.001) were most predictive of lower insurance coverage knowledge. No demographic factors predicted enrollment knowledge. Latino/Hispanic race/ethnicity (p < 0.01) was most predictive of not knowing that more people can get insurance because of the ACA. In conclusion, there is variation in health insurance and ACA-related knowledge in multi-ethnic populations. More compatible health communication interventions are needed to support outreach to key demographic groups.