This paper presents an approach for developing dynamic load model data records for use in planning studies. The load model structure used is the so-called WECC Composite Load Model (CLM). The approach is based on using information about customer classes, various load components in each customer class, and electrical characteristics of each load component. The process is implemented in a tool that can be customized for an individual utility based on its geographical location within the US. Also, the tool can be refined over time due to changing load mix or as more accurate information becomes available. The output of the tool is a dynamic data record for the CLM which can be readily used in dynamic simulations. The main objective of these efforts is to provide an easy-to-use tool for transmission planners to develop load composition for CLM that can be used in time-domain dynamic simulations.