Purpose The purpose of this study was to assess the impact of Diabetes HealthSense on knowledge, attitudes, and behavior changes that prevent, delay, or manage diabetes among people at risk (PAR) for diabetes and people with diabetes (PWD). Methods Using a 2-group pretest-posttest design, 15 community sites were randomly assigned to either an intervention or comparison group. Intervention participants attended a group education session with a diabetes educator, followed by 4 weeks of independent use of the Diabetes HealthSense website. The comparison group received no intervention. A total of 311 adults (n = 135 intervention, n = 176 comparison) completed both a pretest and posttest. Outcome measures examined changes in self-reported knowledge, self-efficacy, and behaviors that support diabetes prevention or management. Results Statistically significant within-group pretest to posttest changes were found for almost all outcome measures in the intervention group, with no significant changes in the comparison group. Significant between-group differences were also found for almost all outcome measures at posttest, with the intervention group having more positive outcomes than the comparison group. Conclusions Patient referral to online tools is considered one key component of initial and ongoing diabetes self-management education and support (DSME/S) and is recommended as a way to enhance and extend the reach of in-person diabetes education. Positive outcomes were found for PWD/PAR who used Diabetes HealthSense following a guided education session. Study results suggested that with guided exploration, Diabetes HealthSense provided a valuable tool for educators to use with patients to support and extend the reach of DSME/S.