Agoncillo is a town and municipality in La Rioja province in northern Spain.

La Rioja is an autonomous community and province in Spain, in the north of the Iberian Peninsula. Its capital is Logroño. Other cities and towns in the province include Calahorra, Arnedo, Alfaro, Haro, Santo Domingo de la Calzada, and Nájera. It has an estimated population of 315,675 inhabitants, making it the least populated autonomous community of Spain.