The high penetration of inverter-based resources (IBRs) will substantially change the dynamic behavior of the power system including inertia distribution. Real-time inertia distribution monitoring is important to support power system operation in future low inertia grids. This article presents the development and validation of a center of power-based inertia distribution estimation technique utilizing the measurements available from the phasor measurement units of the wide-area measurement systems. The suggested technique is validated on the 246-bus northern regional power grid of Indian power system. The impact of different penetration levels of IBRs on the proposed inertia distribution index (IDI) is also studied. The suggested index works purely on power system measurements and does not need any model information. Further, the impact of change in IDI on oscillation baselining study is explored. © 2007-2012 IEEE.