Recent studies have shown that hippocampal “time cells” code for sequential moments in temporally organized experiences. However, it is currently unknown whether these temporal firing patterns critically rely on upstream cortical input. Here we employ an optogenetic approach to explore the effect of large-scale inactivation of the medial entorhinal cortex on temporal, as well as spatial and object, coding by hippocampal CA1 neurons. Medial entorhinal inactivation produced a specific deficit in temporal coding in CA1 and resulted in significant impairment in memory across a temporal delay. In striking contrast, spatial and object coding remained intact. Further, we extended the scope of hippocampal phase precession to include object information relevant to memory and behavior. Overall, our work demonstrates that medial entorhinal activity plays an especially important role for CA1 in temporal coding and memory across time. •MEC was inactivated during temporal, spatial, and object processing in a memory task•CA1 time cells and memory performance were impaired during MEC inactivation•Spatial and object-selective coding remained stable during MEC inactivation•Highly object-selective spiking exhibited theta phase precession Robinson and Priestley et al. combine single-unit recording with large-scale optogenetic inactivation in animals performing a temporal association memory task to assess the role of MEC in the generation of hippocampal temporal, spatial, and object-selective firing fields.