How to register as a vendor with King County

King County posts its solicitations on King County E-Procurement Supplier Portal.^[1] All King County bids and proposals must be submitted in the Supplier Portal, which rejects late submissions.

Changed recently: As of May 23, 2026, all King County suppliers must use multifactor authentication to sign in to the Supplier Portal.^[2]

BidRover has no open bids tagged to King County at the moment. Open bids across Washington are one click away.

1. 01

   Register on E-Procurement Supplier Portal registration

   Start registration. Cost: No fee listed by the County. Upload an IRS W-9 and provide your TIN, Washington UBI, and Washington construction license numbers if applicable. Select NAICS codes for alerts and opt in to rosters; P.O. boxes are not accepted as physical addresses.^[2]

2. 02

   Have your Washington State UBI number

   A Unified Business Identifier is required for portal registration and for SCS certification.^[2]

3. 03

   Choose your commodity codes

   Notifications are sent by the codes in your vendor profile. Pick every code that describes your work, and revisit them when you add a service.

4. 04

   Get certified if you qualify

   Small Contractors and Suppliers (SCS) Certification, through the King County Business Development and Contract Compliance. Free; SBA size standards, $31.84 million three-year gross receipts cap. OMWBE-certified MBE/WBE firms qualify automatically.^[3]

5. 05

   Watch the other buyers

   State agencies in Washington buy through the state portal, and school districts, transit agencies and utilities in the area usually post on their own sites. Registering with King County does not register you with them.

Exact requirements vary by portal; the registration page linked above is the authority. Most ask for:

• Your legal business name and address exactly as registered with the state, and your federal tax ID (EIN, or SSN for some sole proprietors).
• A signed IRS Form W-9, which most buyers collect before they can pay you.
• Commodity codes (NIGP, UNSPSC or NAICS, depending on the portal) for every product and service you sell.
• A contact who will receive bid notices, plus any business license or registration the jurisdiction requires.
• Certificates of insurance and, for construction, bonding capacity: these are usually requested per bid rather than at registration.

• Small capital project work that is not formally advertised goes to firms on the rosters, so opt in when you register.

1. kingcounty.gov/en/dept/executive-services/about-king-county/business-operations/finance-business-operations/procurement-payables
2. kingcounty.gov/en/dept/executive-services/about-king-county/business-operations/finance-business-operations/procurement-payables/supplier-portal
3. kingcounty.gov/en/dept/executive-services/about-king-county/business-operations/finance-business-operations/business-development-contract-compliance/programs/scs-certification