Cisgender Black women in the U.S. have an elevated risk of HIV acquisition, although their adoption of preexposure prophylaxis (PrEP) is low. Studies indicate that increased PrEP knowledge consistently increases the willingness to take PrEP; however, studies on cis Black women are limited. This study aimed to investigate the impact of alcohol and substance use and sexual history on the association between PrEP knowledge and willingness among cis Black women reporting substance use in two emergency departments (EDs). We conducted a secondary analysis of data from 40 HIV-negative cis Black women aged 18–55 years. Using the Anderson Behavioral Model, the variables included predisposing factors (sociodemographic data, PrEP knowledge), enabling factors (income and employment), and disabling factors (alcohol/substance use, condomless sex), with PrEP willingness. Moderation models were used to examine the potential effects of the disabling factors on PrEP knowledge and willingness. The majority (95%) of the participants were PrEP knowledgeable and 52% expressed PrEP willingness. Unemployed participants showed significantly higher willingness to use PrEP and, in multivariate models, were 13.6 times more likely to be PrEP-willing. No significant association was found between PrEP knowledge, frequency of alcohol problems, substance use problems, or condomless sex in the past 30 days. A history of recent alcohol problems, substance use, and condomless sex did not significantly moderate the relationship between PrEP knowledge and willingness among cis Black women. However, employment status was a significant predictor of PrEP willingness and may be important in PrEP uptake decisions. These findings may inform future PrEP interventions and contribute to our understanding of PrEP willingness in HIV-vulnerable populations.