Although Massive Online Open Courses (MOOCs) have the promise to make rigorous higher education accessible to everyone, prior research has shown that registrants tend to come from backgrounds of higher socioeconomic status. In this work, I study geographically granular economic patterns in registration for HarvardX and MITx courses, and in the accuracy of identifying users' locations from their IP addresses. Using ZIP Codes identified by the MaxMind IP geolocation database, I find that per-capit...