COVID-19 has disrupted the lives of many and may have influenced dietary habits through factors such as food security status and attitudes. The purpose of this study was to identify dietary habits and their associations with food insecurity and attitudes among adults living in the United States within three months post-mandated quarantine. An online cross-sectional study was conducted from April to June 2020. Participants (n = 3133) responded to a 71-item questionnaire regarding demographics (n = 7), health information (n = 5), lifestyle habits (n = 8), dietary habits (n = 37), food attitudes (n = 8), and food security status (n = 6). Frequency counts and percentages were tabulated, and multivariate linear regression was conducted to examine associations using STATA v14 at a statistical significance level of p < 0.05. Results showed that most participants indicated no change in dietary habits (43.6–87.4%), yet participants reported increased consumption of sweets (43.8%) and salty snacks (37.4%). A significant positive association for food attitude scores (1.59, 95% CI 1.48 to 1.70; p < 0.001) and food security scores (1.19, 95% CI 0.93 to 1.45; p < 0.001) on total dietary habit scores was found. Future extensive population studies are recommended to help public health authorities frame actions to alleviate the impact that mandated quarantine has on dietary habits.