Differential property tax policy for farmland is often set under conditions of uncertainty and limited information regarding landowners' objective functions. This study examines optimal differential tax policy for a parcel of agricultural land facing uncertain development, identifying instances in which common farmland taxation policies may be non-optimal. Optimal tax rates are characterized given three possible causes of uncertain development: exogenous offers from developers, tax-related reductions in landowner wealth, and a combination of these factors. Model results indicate that underlying causes of uncertain development are critical when seeking to assess the optimality of differential taxation policies, and the use of a single, time-invariant differential tax levy is rarely optimal given uncertain development.