Spodoptera frugiperda is a major pest affecting maize production worldwide, and its control relies heavily on synthetic insecticides, which generate environmental risks and resistance. Essential oils (EOs) represent a promising alternative due to their biodegradability and the biological activity of their terpenoid constituents. This study evaluated the chemical composition, larvicidal activity, and acetylcholinesterase (AChE) inhibitory potential of the EOs from Origanum vulgare, Lavandula dentata, and Mentha piperita against S. frugiperda larvae at the L1, L2, and L4 instars. Chemical characterization by GC–MS revealed distinct chemotypes: a phenolic/terpenoid profile in O. vulgare, a 1,8-cineole-type profile in L. dentata, and a menthol-rich composition in M. piperita. Larvicidal assays showed dose- and stage-dependent responses, and M. piperita EO tended to produce the most robust mortality across instars and times, consistently producing high mortality (75%) at 90 µg·mL−1 air concentration. AChE inhibition assays revealed that carvacrol and menthone were the most active constituents with IC50 values of 312–330 µg·mL−1. Molecular docking supported these results, as carvacrol and menthone showed the most favorable interactions with amino acid residues of the AChE catalytic site. These data support their suitability as candidates for integrated pest management programs targeting S. frugiperda. Future research should focus on formulation strategies, synergistic combinations, detoxification mechanisms, and field validation.