City and county governments do not require SAM.gov registration; it is primarily a federal requirement for federal contracts. The SAM.gov entity registration is a prerequisite for bidding on federal contracts, as an offeror is required to be registered in SAM when submitting an offer or quotation and at the time of award (FAR 4.1102(a); FAR 52.204-7(b)(1)). Federal agencies must also report contract actions over the micro-purchase threshold to the Federal Procurement Data System, which relies on SAM data (FAR 4.606(a)(1)).
State and local governments operate under their own procurement rules, not the FAR. Each state, county, or city typically has its own vendor registration portal and specific requirements. For instance, you mentioned a city portal asking for a tax ID and insurance certificate, while a county form asked for a DUNS number. The Unique Entity Identifier (UEI) did replace the DUNS number for federal contractors as of April 4, 2022. However, some state and local entities may still be transitioning their systems or have not updated their forms to reflect this change. Always check the specific vendor guidelines or procurement office for each local government you plan to work with; they will outline their unique registration and documentation needs.