Embedded piezoresistive microcantilever (EPM) sensors provide a small, simple and robust platform for the detection of many different types of analytes. These inexpensive sensors may be deployed in battery-powered handheld units, or interfaced to small, battery-powered radio transmitter-receivers (motes), for deployment in mesh networks of many sensors. Previously, we have demonstrated the use of EPM sensors in the detection of hydrogen fluoride gas, organophosphate nerve agents, volatile organic compounds (VOC’s), chlorinated hydrocarbons in water, and others. Here, we report on the design of EPM sensors functionalized for the detection of chlorine gas, or Cl2. We have constructed EPM sensors using composite materials consisting of a polymer or hydrogel matrix loaded with agents specific for the detection of Cl2 such as NaI. These materials were tested in both controlled laboratory conditions and in outdoor releases. Stability of the sensing materials under conditions of high temperature were also studied. Results are presented for gas exposures ranging from 1000 ppm to 20 ppm.