This study presents a comprehensive analysis of time evolution and spatial distribution of crystallographic geometrically necessary dislocation (GND) density induced by solid-state thermal cycling in an IN718 polycrystal. A thermomechanical crystal plasticity finite element model is employed to capture the thermal-stress response under a simulated single-step thermal cycle. Two distinct methodologies for calculating GND density are explored and compared: one based on the plastic deformation gradient and the other on the orientation gradient. This computational approach expands existing postmortem and 2D experimental analyses by providing a fully time-resolved, three-dimensional perspective on the evolution of lattice rotations and dislocation densities under thermal cycling without external mechanical loading.