Background: The task of monitoring and managing the entire emergency department (ED) is becoming important to the ED staff since EDs get increasingly crowded and treatments become more complex. Recently, dashboards have received the spotlight as health information technology to support these tasks. Objective: This study aimed to describe the process of developing a real-time comprehensive dashboard for ED and to evaluate its usability by clinical staffs. Methods: We developed a dashboard based on three dashboard principles -"anytime, anywhere, at a glance"; "minimal interruption to workflow"; and "protect patient privacy"-and three design concepts-"geographic layout," "patient-level alert," and "real-time summary data." The measurements on the dashboard were selected based on the throughput factor of the conceptual model of ED crowding. We also surveyed ED physicians and nurses using a system usability scale (SUS) and situation awareness index, a questionnaire we created based on the construct of the situation awareness rating technique. Results: The first ED dashboard was successfully launched in 2013 and has undergone three major revisions because of geographical change to the ED and to improve usability. A total of 52 ED staff members participated in the survey. The average SUS score of the dashboard was 67.6 points. The participants also evaluated the dashboard as good at "concentration support" (4.15), "complexity representation" (4.02), "variability representation" (3.96), "information quality provided" (3.94), and "familiarity of dashboard" (3.94). However, the "division of attention" was rated 2.25 points. Conclusions: We developed the ED dashboard and successfully used it for five years. The ED physicians and nurses evaluated its usability as "OK to Good."