Few economic analyses examine land trusts, their decisions, and the land-trust “industry,”despite their growing importance. For example, statistics on the wide variation in thenumber of trusts in different regions of the United States raise questions about whethersuch variation makes economic sense. This paper builds a model to identify the optimalnumber of private conservation agents. The model depicts two competing forces: regionalspatial externalities in conservation benefits that increase the efficiency of having feweragents and organizational costs, and fund-raising specialization, which increases theefficiency of having more agents. Using state-level variables, we perform a count-dataanalysis of the number of trusts conserving land in each state. We find that the number oftrusts actually observed is consistent with the optimal number of trusts that is predictedby the model on the basis of the relative importance of spatial externalities andorganizational size in different regions.