Highways consist of many large structures requiring vigilant inspection and maintenance. While significant research attention has been focused on the health management of bridges, comparatively less attention has been paid to other highway structures including retaining walls. In the United States, there has been a recent emphasis on extending the use of risk management methods to the extremely large national inventory of retaining wall structures. In this paper, a long-term wireless monitoring system is developed as a cost-efficient approach to collecting data and information required for risk assessment of retaining wall structures. The study focuses on two reinforced concrete (RC) retaining walls to highlight the monitoring system design and to illustrate how measurement data offers insight to wall performance. The first wall is a caisson supported retaining wall along the M-10 freeway in Detroit, MI; the second is a classical reinforced concrete cantilever wall along I-696 in Southfield, MI. The wireless monitoring system installed on each wall system uses a cellular-based wireless sensor node termed Urbano that is solar powered and customized to measure wall tilt using inclinometers, wall strain using strain gages, and wall temperature using thermistors. The monitoring systems have been valuable in assessing the behavior of the M-10 and I-696 wall systems for a broader risk management framework. The monitoring results reveal both wall systems are operating as designed with limited tilt and strain responses to normal environmental factors including moisture and temperature.