Background: Diabetes mellitus (DM) is a chronic metabolic disease resulting from either a deficit in insulin secretion (type 1) or a function (type 2) that results in an increased level of glucose in the blood. Diabetes mellitus increases the risk for developing many serious complications including microvascular, macrovascular, decreased reproductive activity, and frequent infections. Objective: The aim of this study was to assess the awareness level regarding DM risk factors, symptoms, signs, management, and complications in both the diabetic and the nondiabetic population. Method: This cross-sectional, descriptive study was conducted among the general population of Jeddah, Saudi Arabia, in 2019. A total of 24 questions from a pre-piloted questionnaire were interpreted into Arabic. The questionnaire contained a series of questions arranged in four parts: Assessing DM general knowledge, risk factors, symptoms, and complications. Result: This study included 1324 participants; 52.5% were female. The largest age range among the participants (41.5%) was 15–23 years, followed by the 44–53 (18.8%) year age group. Regarding the questions answered correctly: a total mean score achieved by the whole population was 13.9 ± 3.6 out of 19 points (73.9 ± 19.3%). The diabetic participants achieved higher scores than the nondiabetics in each category. Conclusion: The study found that the largest gap in knowledge regarding DM is in the knowledge of its complications. The role of health education needs emphasis at all levels starting with schools and universities. This is in addition to general public health education, distributing knowledge through brochures and social media.