Can India’s official statistics detect large-scale undocumented migration? Undocumented migrants may evade law, but can they evade the Census? If millions of them are living in India, they must appear somewhere in the country’s official statistics. Union Minister of Parliamentary Affairs Kiren Rijiju told Parliament that “As per available inputs, there are around 20 million illegal Bangladeshi migrants staying in India”. Then, they must come across enumerators during the Census. Millions of such people then must be meeting enumerators during the decennial censuses of India. What might an undocumented migrant do in such an encounter? They can respond in three ways: avoid or duck the Census altogether, contributing to coverage error; be counted but report India rather than Bangladesh as the place of birth, creating measurement error; or report the place of birth truthfully. Each of these choices leaves a different mark in the data, which can be checked. Together, this provides a simple framework for asking whether India’s official data are consistent with the claimed scale of undocumented migration. But a framework based on …