Background Older adults living in social housing are a vulnerable population facing unique challenges with health literacy and chronic disease self-management. We investigated this population’s knowledge of cardiovascular disease and diabetes mellitus, and self-efficacy to make health behaviour changes (for example, physical activity). This study characterized the relationship between knowledge of health risk factors and self-efficacy to improve health behaviours, in order to determine the potential for future interventions to improve these traits. Methods A cross-sectional study (health behaviour survey) with adults ages 55+ (n = 599) from 16 social housing buildings across five Ontario communities. Descriptive analyses conducted for demographics, cardiovascular disease and diabetes knowledge, and self-efficacy. Subgroup analyses for high-risk groups were performed. Multivariate logistic regressions models were used to evaluate associations of self-efficacy outcomes with multiple factors. Results Majority were female (75.6%), white (89.4%), and completed high school or less (68.7%). Some chronic disease subgroups had higher knowledge for those conditions. Significant (p < 0.05) associations were observed between self-efficacy to increase physical activity and knowledge, intent to change, and being currently active; self-efficacy to increase fruit/vegetable intake and younger age, knowledge, and intent to change; self-efficacy to reduce alcohol and older age; self-efficacy to reduce smoking and intent to change, ability to handle crises, lower average number of cigarettes smoked daily, and less frequent problems with usual activities; self-efficacy to reduce stress and ability to handle crises. Conclusions Those with chronic diseases had greater knowledge about chronic disease. Those with greater ability to handle personal crises and intention to make change had greater self-efficacy to change health behaviours. Development of stress management skills may improve self-efficacy, and proactive health education may foster knowledge before chronic disease develops.