The approximately number system (ANS) helps people quickly estimate the numerosity of objects in their environment. In this study, we explore one proposed mechanism for visually perceiving numerosity: visual clustering. Participants completed a magnitude comparison task, magnitude estimation task, and a clustering task using the same set of numerosity stimuli. The stimuli varied in the spatial configuration of the points (cluster structure -- clustered or dispersed) and in the number of points present. Participants judged stimuli with dispersed cluster structure to be more numerous in the magnitude comparison task. However, there was a minimal effect of cluster structure in the magnitude estimation task and no effect of the number of clusters perceived in both tasks. We also found that the clusters people perceived in the third task did not explain the effects of cluster structure. These findings go against strong claims that people use visual clustering to judge numerosity and set the stage for further investigations into the mechanisms underlying the ANS.