Land subsidence involves either elastic (recoverable) or inelastic (unrecoverable) soil compaction within an aquifer. Elastic or inelastic subsidence is tradionallly identified on the basis of the relation between deformation and hydraulic head changes. This study aims to determine the statistical hydraulic head rule for inelastic subsidence mitigation in groundwater management. By focusing on Yunlin County in Taiwan as the study area, this research effectively distinguishes between unrecoverable and recoverable subsidence using the head rule with the statistical threshold, which is calibrated by an optimal linear search. Result shows that considering the head rule can obtain similar patterns of subsidence with the traditional model from the stress–strain diagram. Inelastic subsidence accounts for approximately 15% of all instances, notably occurring during the early months of each year. Inelastic subsidence usually happened in the mid-fan and distal fan. This study can rapidly identify when and where unrecoverable subsidence happens. Groundwater management within the head threshold would be implemented for unrecoverable subsidence mitigation.