Des Moines Auto Co. - began operations in 1918, in 1928 merged into Suburban Transit System. Service operated between Seattle and Des Moines.
Haller Lake Transportation Co. - began operations in 1926, in 1928 merged into Suburban Transit System. Service operated north of Seattle, adjacent to Haller Lake.
Seattle Motor Coach Co. - formed in 1921 by acquiring North End Transportation Line, in 1928 merged into Suburban Transit System. Route operated between Seattle and Country Club via Greenwood Ave.
Yost Auto Co. - formed in 1915, acquiring operation introduced in 1913 by Ellington Brothers, in 1928 merged into Suburban Transit System. Route operated between Seattle and Edmonds, which is in Snohomish County whose Community Transit assumed a portion of the service.
Seattle-Renton Stage Line - began operations in 1922, in 1938 renamed Renton-Bothell-Seattle Stage Line, in 1943 renamed Lakeshore Lines. Service operated between Seattle and Renton. A second service introduced in 1923 operated between Seattle and Bothell.
North Bend Stage Lines - began operations in 1919, in 1925 acquired Preston-Issaquah-Seattle Stage Line and Cascade Mountain Stage Line, in 1953 routes transferred to Lakeshore Lines. Route operated between Seattle and North Bend.
Black Diamond Stage Co. - in 1946 acquired by Lakeshore Lines. Route operated through Green River Gorge serving Maple Valley and Ravensdale, discontinued prior to 1973 Metro takeover, although Metro later expanded into the area.
Overlake Transit Service - began operations in 1927. Original service operated between Roanoke and Beaux Arts. And in 1936, service was expanded to serve Medina, Bellevue, and south end of Lake Sammamish.
In 1963, Overlake Transit Service acquired Suburban Transit System and Lakeshore Lines, and became a subsidiary of American Transit Corp. And in 1965, Overlake Transit Service acquired Greyhound's suburban routes to Everett, and to Kent, Auburn, and Tacoma. Metropolitan Transit Corp. was formed as a new company to operate all of the Seattle area's suburban bus routes. Metropolitan Transit Corp. became part of King County Metro in 1973.
Additional obscure bus companies previously existed, according to the 1952 "Mass Transportation's Directory", and the WPA American Guide Series of state guidebooks.