So where are the 1st, 2nd, 5th and 8th? you ask.
The 1st is in Snohomish County, the 2nd in Pierce and Thurston counties, and the 5th in King County. The 8th is on the western edge of the 9th, although far removed from the 7th.
At the start of statehood, the numbering of legislative districts followed a pattern that started with the 1st District in north-central Washington at the east slope of the Cascades and moved more or less clockwise around the state. The counties to the north of Spokane County were the 2nd District, Spokane County was home to the 3rd through the 7th, Whitman County had the 8th and 9th, the 10th covered the southeast counties before the numbers moved west along the state’s southern boundaries then north up the Olympic Peninsula, then up the east side of the Puget Sound.
Some shrank and some expanded because of population growth, but they stayed pretty much in place. In 1931, the state started adding legislative districts to the fast-growing areas of the Puget Sound, but most were at least fairly close to the other top numbers, so the single digits and teens stayed on the East Side. They did, however, have to drop a newly created 49th District into Vancouver in 1957.
That general numeric consistency ended in 1965 when the 1st District was moved from Okanogan County to King County as part of the redistricting and Okanogan was combined with Ferry, Stevens and Pend Oreille counties in the 2nd District. The 2nd was moved to Pierce County in 1972 and the 7th, which had been the West Plains and other rural parts of north Spokane County, was expanded to hold much of the previously combined 2nd District.