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King County's street naming and numbering system developed over the course of the twentieth century. It was aimed at developing a clear and concise street designation system intended to lend increased facility to the location of addresses. A numbered grid pattern of avenues and streets, an extension of and compromise with the City of Seattle's street system, is the centerpiece of the system.

The system had its beginning in 1920 and 1921 with the passage of two Commissioners' resolutions (690, 730) which extended the grid north and south from what were then the city limits of Seattle. The next surge followed in 1930 with the adoption of two more sizable resolutions (3709, 7558) which further extended the grid south and north of Seattle. Preference was given to numbered avenues and streets rather than named roads.

Resolution 16622 (August 13, 1956) extended the grid numbering system countywide and is considered the base legislation for all amending resolutions and ordinances that followed. This resolution authorized the use of numbers to replace names as often as possible.

Names were retained on some roads and some new names are still assigned. Names are used where they have meaningful geographical significance, or for roads that deviate too widely from the grid system to make numbers practical. A name is not retained or a new name is not assigned if a number designation fits the grid system.

The King County Archives retains copies of all road name resolutions and ordinances in its legislative files. The road name changes are set out in the resolution or ordinance by section-township-range coordinates, and states the former and new name of each road. Please contact the Archives for further information.

The Archives also holds records relating to Vashon Island road name changes:

Project file: Vashon-Maury Island street addressing, 1988-1991

To improve emergency response access to locations on Vashon and Maury Islands, in 1988 King County initiated a street measurement and address assignment project. The project, which changed most named streets to numbered ones. It was undertaken by a team of local residents under general direction of the Building and Land Development (BALD) Division. This file consists of a manual and project history compiled at BALD's request by geodata technician Ken Brooks. The manual comprises text sections illustrated with copies of forms, worksheets, maps, correspondence, etc.; section topics include socio-cultural background and community information; measuring and recording fieldwork; road designations; address number assignment; map and sign preparation; quality checks; and project wrap-up. Two appendices include copies of Vashon/Maury Island newspaper articles, and photocopied snapshots of project participants.

For questions, or to access this series, please contact the Archives.

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Please note the Archives is closed Wednesdays.