The tri-state water battle between Georgia, Alabama and Florida, the continuing drought in the southeastern USA, and the rapidly increasing irrigated acreage in agriculture are some of the current issues affecting water use in the state of Georgia. An understanding of present and future water needs by agriculture is needed to ensure availability of water for current and future users. Unfortunately, how much water is required and how much is actually being used for irrigation is not known. The objective of this study is to predict the current irrigation demand for the entire state of Georgia using crop simulation model linked to a geographic information system (GIS) that includes spatial weather and soil data bases. Traditionally, crop simulation models have been applied to a field or a farm level where the spatial variability of the environment is not considered. Linking crop simulation model with GIS extends the capabilities of the crop model to a regional level. The entire agricultural area in Georgia is partitioned into smaller areas where the hydrologic processes and the soil, weather and crop can be considered uniform or characterized by simple relationships. A crop simulation model, which has soil and plant water balance and potential evapotranspiration components, is used for each of these smaller areas to determine actual crop evapotranspiration and irrigation demand. Spatial distributions of irrigation demand across the state of Georgia are presented and analyzed as they are impacted by local weather and soil conditions.