This work presents the development and evolution of the test cell (TC) neutronics geometry models for IFMIF-DONES (International Fusion Materials Irradiation Facility–Demo Oriented Neutron Source), supporting detailed Monte Carlo–based nuclear analyses for design assessment and optimization. Beginning with the IFMIF/EVEDA configuration, successive model versions have been developed to reflect major DONES design updates, including the design changes to a single accelerator and test module, revised target assembly (TA) and High Flux Test Module (HFTM) designs, relocation of the quench tank, and the introduction of removable biological shielding blocks (RBSBs). To balance modeling accuracy and computational efficiency, both high-fidelity and lightweight geometry representations were investigated. Sensitivity studies on geometry boundaries and levels of simplification demonstrate that key irradiation performance metrics, such as neutron flux and damage doses, are well preserved when essential TA and HFTM features are retained. Simplified yet representative target and HFTM models were validated for use in accelerated simulations. In parallel, an unstructured mesh-based HFTM model was successfully implemented and benchmarked against conventional CSG-based models, showing excellent agreement.