[en] Fe vacancies in the 33 K superconductor K_1−xFe_2−ySe₂ show ordering schemes that may be correlated with its superconducting properties. First-principles calculations and kinetic Monte Carlo simulations lead to a very simple model for vacancy ordering. Repulsive dipolar interactions between Fe vacancies show three ground states: a $\sqrt{8}\times <!--\; ??\; -->\sqrt{10}$ rhombus-ordered structure for 12.5% vacancies, a $\sqrt{5}\times <!--\; ??\; -->\sqrt{5}$ squared lattice for 20% vacancies, and a $\sqrt{5}\times <!--\; ??\; -->\sqrt{5}$ rhombus-ordered structure for 25% vacancies. Other structural states are derived from these three ground states and may contain additional disordered spatial regions. The repulsive interaction between Fe vacancies arises from enhanced Fe–Se covalent bonds, which differs from the well-known attractive interaction of Fe vacancies in body-centered cubic Fe. (paper)