Electric-field-driven oxygen ion evolution in the metal/oxide heterostructures emerges as an effective approach to achieve the electric-field control of ferromagnetism. However, the involved redox reaction of the metal layer typically requires extended operation time and elevated temperature condition, which greatly hinders its practical applications. Here, we achieve reversible sub-millisecond and room-temperature electric-field control of ferromagnetism in the Co layer of a Co/SrCoO2.5 system accompanied by bipolar resistance switching. In contrast to the previously reported redox reaction scenario, the oxygen ion evolution occurs only within the SrCoO2.5 layer, which serves as an oxygen ion gating layer, leading to modulation of the interfacial oxygen stoichiometry and magnetic state. This work identifies a simple and effective pathway to realize the electric-field control of ferromagnetism at room temperature, and may lead to applications that take advantage of both the resistance switching and magnetoelectric coupling.