GIS is a technology with the potential to transform government by enhancing business processes and providing a platform to manage spatial and non-spatial data, which is expected to result in better decision-making. However, little is known about how this technology is actually implemented organization-wide and the environment surrounding its use. Current GIS maturity models have not examined usage broadly or in-depth, lack empirical validation, and measurement tools to diagnose maturity are not readily available. Based on GIS, maturity models, and system usage literature this study presents a more comprehensive maturity model for evaluating local government usage of GIS along with a measurement tool. The study followed De Bruin guidelines for developing maturity models. This new model was discussed with practitioners and academics, was pilot-tested, and then widely tested on Southern California local governments through an online questionnaire. Results show support for the validity of the model and demonstrate its utility.