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This work explores the 2D interfacial energy transport between monolayer WSe₂and SiO₂while considering the thermal nonequilibrium between optical and acoustic phonons caused by photoexcitation. Recent modeling and experimental work have shown substantial temperature differences between optical and acoustic phonons (ΔT_OA) in various nanostructures upon laser irradiation. Generally, characterizations of interfacial thermal resistance (R′′_tc) at the nanoscale are difficult and depend on Raman‐probed temperature measurements, which only reveal optical phonon temperature information. Here it is shown that ΔT_OAfor supported monolayer WSe₂can be as high as 48% of the total temperature rise revealed by optothermal Raman methods—a significant proportion that can introduce sizeable error toR′′_tcmeasurements if not properly considered. A frequency energy transport state‐resolved Raman technique (FET‐Raman) along with a 3D finite volume modeling of 2D material laser heating is used to extract the true interfacial thermal resistanceR′′_tc(determined by acoustic phonon transport). Additionally, a novel ET‐Raman technique is developed to determine the energy coupling factorGbetween optical and acoustic phonons (on the order of 10¹⁵W m⁻³K⁻¹). This work demonstrates the need for special consideration of thermal nonequilibriums during laser–matter interactions at the nanoscale.