The discourse around indigeneity, customary rights of possession and claims to political autonomy in Northeast India conventionally traces the postcolonial protectionist legislation for ‘tribes’ to various acts passed under the late colonial state, the most significant precursor being seen as the Government of India Act, 1935. This article will argue that one can in fact trace the ‘original moment’ in the idea of customary law for ‘tribes’ much further back in history, to the early decades of the nineteenth century. This historical moment was anchored in the beginnings of the East India Company’s conquest of the Garo hills in the late eighteenth and early nineteenth centuries, in the appropriation of the land and revenue of the Garos and in the ethnogenesis of the ‘hill Garo’. The article will explore the ways in which the beginning of the invention of customary law and traditional authority in Northeast India under East India Company rule was impelled by the Company’s demands for revenue and was shielded and secured by the deployment of military power across the hills. Over the course of the nineteenth century, the strategies of imperial control first introduced in the region were reproduced across the rest of Northeast India, underscoring the significance of the Garo hills as the first ‘laboratory’ of colonial rule in the region as well as sharpening our understanding of the character of the early colonial state. The article thus takes as its task the historicization of the categories of ‘customary law’, ‘traditional/indigenous authority’ and the ‘hill tribe’, all of which form the basis of late colonial and postcolonial legislation on the ‘tribe’.