When producing creative ideas (i.e., ideas that are original and useful) two main processes occur: ideation, where people brainstorm ideas, and evaluation, where they decide if the ideas are creative or not. While much is known about the ideation phase, the cognitive processes involved in creativity evaluation are less clear. In this article, we present a novel modeling approach for the evaluation phase of creativity. We apply the drift diffusion model (DDM) to the Creative-or-Not task (CON-task) to study the cognitive basis of evaluation and to examine individual differences in the extent to which people take originality and utility into account when evaluating creative ideas. The CON-task is a timed decision-making task where participants indicate whether they find uses for certain objects creative or not (e.g., using a book as a buoy). The different uses vary on the two creativity dimensions "originality" and "utility." In two studies (n = 293, 17,806 trials; n = 152, 9,291 trials), we found that stimulus originality was strongly related to participants' drift rates but found only weak evidence for an association between stimulus utility and the drift rate. However, participants differed substantially in the effects of originality and utility. Furthermore, the implicit weights assigned to originality and utility on the CON-task were associated with self-reported importance ratings of originality and utility and with divergent thinking performance in the Alternative Uses task (AUT). This research provides a cognitive modeling approach to creativity evaluation and underlines the importance of communicating rating criteria in divergent thinking tasks to ensure a fair assessment of creative ability. [This research was presented at the virtual MathPsych/ICCM conference in 2020.]