2D ferromagnets have attracted considerable attention due to their strong potential in the post‐Moore Law era. However, intrinsic 2D ferromagnetic materials typically suffer from suppressed Curie temperature due to thermal fluctuation, magnetic order instability in the 2D limit, and others. Herein, a nonmagnetic fluorine modification strategy is proposed to control the ferromagnetism of air‐stable antimonene. It is demonstrated that fluorinated antimonene (F‐antimonene), synthesized via an electrochemical exfoliation and synchronous fluorination method, exhibits robust ferromagnetism with a Curie temperature of up to 717 K (compared with a Curie temperature of 220 K for pristine antimonene) and a saturation magnetization of ≈0.1 emu g⁻¹ (determined by the fluorination degree). First‐principles simulations confirm that the robust long‐range ferromagnetic order in the half‐metallic F‐antimonene is induced by the low‐density sp‐electron‐polarized impurity subbands. The study constitutes a nonmagnetic control of robust above‐room‐temperature ferromagnetism in monoelemental 2D semiconductors and paves a new route toward 2D atomic layer‐based spin devices.