Advances in sensing and communication technologies are enabling new applications for providing more effective health care. In particular, systems that focus on prevention by continuously and remotely monitoring patients and their surroundings can improve healthcare quality and ease the task of healthcare professionals. This paper describes a Health IT Testbed that provides a comprehensive framework for monitoring a healthcare facility and provides a visualization interface to peruse this data. The testbed comprises two subsystems, a sensing subsystem and a visualization subsystem. The sensing system is responsible for collecting patient and ambient data, and is organized in a hierarchical fashion. For fine-grained physical entity sensing (e.g., sensing body postures of patients), we use SunSPOT wireless modules and a state machine approach to detect the current state of patients. For system-level sensing (e.g., state of the entire healthcare facility), we have created a Crossbow Motes wireless modules based infrastructure, and used a graph-based approach to detect current state and movement of entities between physical spaces. The monitoring system correlates various sensor data to populate a database with information regarding the state of the patients and the surrounding systems. The visualization system takes its input from the database being populated by the monitoring system and allows users to peruse both real-time and historical data. We also present performance results to evaluate the system.