The technology is generally directed towards characterizing primary frequency response parameters (e.g., frequency response coefficient, inertia, damping, droop) for an interconnection, region, and power plant utilizing phasor measure unit (PMU) data captured during an event (e.g., a generation trip event) that causes an imbalance in the power grid system. Pre-processing of localized PMU based frequency measurements combined with system identification techniques fit the observed frequency response to estimate parameters such as system inertia, frequency response coefficient, turbine time constant, system damping and governor droop that characterize the interconnection-wide frequency response.