The Portland post office was established on November 8, 1849, almost a decade before statehood, with Thomas Smith as postmaster. Salem’s was established the same day, with John B. McClane postmaster.
According to the Earliest Oregon Postoffices as Recorded at Washington (by Lewis A. McArthur in the Oregon Historical Quarterly Vol. 41, No. 1 – March 1940), which used as its source Book 19 of “a series of volumes in the office of the Division of Postmasters’ Appointments at the Post Office Department in Washington, D. C.”, the Salem and Portland post offices were the third and fourth in Oregon, after those in Astoria (March 9, 1847) and Oregon City (March 29, 1847).