Hundreds of studies in economics misinterpret China's subnational population and per capita data. The most widely used population counts are of hukou registrations from each province, prefecture, county, or city rather than of the people living in each place and generating local gross domestic product. Over 220 million people have left their place of registration, while almost none had when reforms began, creating time‐varying errors in estimates of per capita income of subnational units. We survey empirical articles in blue ribbon journals, in development journals, and in regional and urban economics journals that use China's subnational data. Over 80% of articles use these data erroneously; most commonly the wrong population or employment counts are used to measure the size of subnational units, and per capita data are calculated with the wrong denominator for how variables are interpreted. We provide examples of errors from each group of journals, and a critical test of one highly cited study. Specifically, we show that if hukou registrations are erroneously used to measure the local population, following existing practice, conclusions about driving forces for urban area expansion are reversed. We give recommendations for more careful use of China's subnational population and per capita data.