ABSTRACT: Irrigated agriculture has emerged as a necessary technology to achieve greater productivity, mainly by supplying the water requirements of agricultural crops in critical periods, especially for those regions where natural rainfall is insufficient to meet these requirements. The daily water consumption of crops is strongly influenced by local weather conditions, which justifies the need for regionalized studies of the parameters influencing the water depth to be applied. The crop coefficient (Kc) is perhaps the most important parameter because it interferes directly with the crop water requirements. This index must be determined for each region, thus avoiding the use of reference values meant for other climatic conditions, causing loss of productivity The present study aimed to estimate the local crop coefficients for corn (Zea mays L.) for the climatic conditions of the State of Maranhão, aiming at the rational use of water in agriculture. The method, which allowed obtaining the local values of Kc for different phases of the crop cycle, used climatic data from 12 weather stations (INMET) and mathematical equations proposed by Albuquerque et al. (2001). It estimated the mean and final Kc values. The local values of Kc obtained for corn ranged from 0.73 to 0.77, 1.00 to 1.31, and 0.24 to 0.45 for initial, intermediate, and final phases, respectively.