This military had a very short history, all of which seems to have been spent in the state of Washington. The unit did not see service abroad.
The Washington Volunteer Infantry Battalion was mustered into service at Tacoma, Washington between July 2 and July 15, 1898. At the time of muster in, the unit consisted of fourteen officers and 412 enlisted men. The unit, commanded by Colonel Wholly, remained a battalion because it only ever consisted of four companies, instead of the usual ten to thirteen companies that would comprise a regiment. The unit formed quite late, since the fighting ended on August 12, 1898 when an armistice was declared.
From its official mustering, the 1st Washington Volunteer Infantry Battalion was held in reserve at the Vancouver Barracks. In September, the unit was replaced by the 8th California Volunteer Infantry. It is not clear if the men were furloughed at this point, however, but the commander of the Department of Columbia, which included Washington, makes no further note of the unit.
The unit was mustered out at Vancouver Barracks on October 28, 1898. At the time of muster out, the unit consisted of almost the same number of officers and men, experiencing a net loss of one enlisted man. During its term of service lost one man who died of disease, two more who were discharged on disabilty, and four men who deserted.
The War ended on December 10, 1898, with the signing of the Treaty of Paris.
Clerk of Joint Committee on Printing, The Abridgement of Message from the President of the United States to the Two Houses of Congress. (Washington: Government Printing Office, 1899). Vol. 3, 181.
Statistical Exhibit of Strength of Volunteer Forces Called into Service During the War with Spain; with Losses from All Causes. (Washington: Government Printing Office, 1899).