Mennecy is 33 kilometers south east of Paris-Notre-Dame, point zero from roads of France, 8 kilometers south of Évry, 6 kilometers south west of Corbeil-Essonnes, 11 kilometers north east of La Ferté-Alais, 14 kilometers east of Arpajon, 15 kilometers south east of Montlhéry, 19 kilometers north of Milly-la-Forêt, 22 kilometers south east of Palaiseau, 25 kilometers north east of Étampes, 31 kilometers north east of Dourdan. It is crossed by the riverEssonne.