OMSSA's members are Ontario's 47 Service System Managers (Consolidated Municipal Service Managers (CMSMs) and District Social Services Administration Boards (DSSABs), including:
District of Manitoulin-Sudbury (DSSAB)
District of Parry Sound (DSSAB)
District of Rainy River (DSSAB)
District of Sault Ste. Marie (DSSAB)
District of Thunder Bay Social Services Administration Board (TBDSSAB)
District of Timiskaming (DSSAB)
Prince Edward-Lennox and Addington Social Services (PELASS)
Regional Municipality of Durham
Regional Municipality of Halton
Regional Municipality of Niagara