Joint districts may be established containing all or part of two or more counties. The county containing the largest portion of the population of a joint district shall be known as the "principal county" and each joint district shall be deemed to lie within the principal county for the purpose of chapters 3.30 through 3.74 RCW. A joint district may be established by resolution of one county concurred in by a resolution of each other county: PROVIDED, That the county legislative authority of a county containing the largest portion of the population of a city may include the portions of such city lying outside the county in a joint district without concurrence of the other counties.
Elections of judges in joint districts shall be conducted and canvassed in the same manner as elections of superior court judges in joint judicial districts.