The mentalizing network is theorized to play a central role in making sense of people (compared with nonsocial targets), but is its involvement affected when we make sense of people in a nondispassionate manner (e.g., favoritism toward others on the basis of group membership)? First, mixed findings and small samples have prevented strong conclusions about whether intergroup evaluation increases or decreases activation regions associated with the mentalizing network. Second, little is known about the psychological mechanism underlying mentalizing network activation shaped by ingroup versus outgroup evaluations. Psychological models suggest two hypotheses that can be challenging to disentangle with self-report: Ingroup trait evaluations may benefit from a priori expectations and/or preferential evidence accumulation. Therefore, the current study (n = 50) drew on a combination of drift diffusion modeling and fMRI to examine how group membership affects the engagement of the mentalizing network for trait evaluation and whether group-differentiated activation is associated with a priori expectations and/or preferential evidence accumulation. Outgroup trait evaluations engaged dorsomedial pFC activation, whereas ingroup trait evaluations engaged ventromedial pFC activation as well as other regions associated with mentalizing such as precuneus, posterior cingulate cortex, and right TPJ. Furthermore, the ventromedial pFC and posterior cingulate cortex activation was associated with differential expectations applied to ingroup trait evaluation. The current findings demonstrate the importance of combining motivational factors, computational modeling, and fMRI to deepen our understanding of the neural basis of person evaluation.