We developed micromolded microwell arrays to study the proliferation and senescence of single cells. Microwell arrays were designed to be compatible with conventional cell culture protocols to simplify cell loading, cell culture, and imaging. We demonstrated the utility of these arrays by measuring the proliferation and senescence of isogenic cells which expressed or had been depleted of the human Werner syndrome protein. Our results allowed us to reveal cell-to-cell heterogeneity in proliferation in WRN+ and WRN-depleted fibroblasts during clonal growth.