Recent evidence suggests that epigenetic mechanisms may contribute to memory deficits in aging. Specifically, in the hippocampus, the repressive epigenetic mark H3K9me3 (tri-methylated lysine 9 on histone H3) has been implicated in the silencing of genes essential for memory. Yet, the impact of the age-related increased H3K9me3 levels on neuronal function remains unclear. We hypothesized that H3K9me3 accumulation renders neurons refractory to stimulation. To assess the influence of H3K9me3 on neuronal activation, we reduced H3K9me3 levels by silencing the major methyltransferase responsible to produce H3K9me3 (SUV39H1) using shRNA delivered via an adeno-associated virus (AAV) in the dorsal dentate gyrus. For modeling stimulation, male mice were exposed to a novel environment for 15 min, and neuronal activation was assessed 1-hour later by measuring the presence of the Arc protein. Immunohistochemistry and flow cytometry data confirmed that the shRNA-SUV39H1 delivery reduced H3K9me3 levels in transfected neurons (tagged with EGFP) compared to non-transfected ones. Furthermore, we observed a significant increase in the percentage of activated neurons in the shRNA-SUV39H1 transfected population, suggesting an enhanced capacity for neuronal activation in response to the reduced levels of H3K9me3. Our findings suggest that the inhibition of SUV39H1 facilitates neuronal activation by decreasing the repressive H3K9me3 mark. Additionally, our data support the concept that epigenetic regulation through H3K9me3 plays a role in the decline of hippocampal-dependent memory with age.