The pathways that lead to the development of tissue-resident lymphocytes, including liver type 1 innate lymphoid cells (ILC1s), remain unclear. We show here that the adult mouse liver contains Lin(-)Sca-1(+)Mac-1(+) hematopoietic stem cells derived from the fetal liver. This population includes Lin-CD122(+)CD49a(+) progenitors that can generate liver ILC1s but not conventional natural killer cells. Interferon-gamma (IFN-gamma) production by the liver ILC1s themselves promotes the development of these cells in situ, through effects on their IFN-gamma R+ liver progenitors. Thus, an IFN-gamma-dependent loop drives liver ILC1 development in situ, highlighting the contribution of extramedullary hematopoiesis to regional immune composition within the liver.