1890s County places a bounty on wolves, wildcats and mountain lions.
1902 Mason installs its first telephone in the county judge's office.
1913 County hires an agricultural agent.
1918 October 3 – Eighteen months after United States Congress declares war on Germany, the Mason County Council of Defense draws up resolution to abandon the use of the German language in the county. The majority of County residents are of German heritage.
1919 First oil and gas lease in the county. Construction begins on the Mason County section of the Puget Sound-to-the-Gulf Highway.
There were 1,607 households of which 25.90% had children under the age of 18 living with them, 59.10% were married couples living together, 7.70% had a female householder with no husband present, and 30.90% were non-families. 29.20% of all households were made up of individuals and 17.90% had someone living alone who was 65 years of age or older. The average household size was 2.31 and the average family size was 2.83.
22.40% of the population were under the age of 18, 4.70% from 18 to 24, 20.70% from 25 to 44, 28.80% from 45 to 64, and 23.50% who were 65 years of age or older. The median age was 47 years. For every 100 females there were 92.40 males. For every 100 females age 18 and over, there were 87.60 males.
The median household income was $30,921 and the median family income was $39,360. Males had a median income of $28,125 compared with $20,000 for females. The per capita income was $20,931. About 10.10% of families and 13.20% of the population were below the poverty line, including 20.50% of those under age 18 and 13.30% of those age 65 or over.
^ abLehmann, Herman; Hunter, J Marvin; Giese, Dale F (1993). Nine Years Among the Indians, 1870–1879: The Story of the Captivity and Life of a Texan Among the Indians. University of New Mexico Press. ISBN978-0-8263-1417-8.
^Johnson, David; Miller, Rick (2009). The Mason County ""Hoo Doo"" War, 1874–1902 (A.C. Greene Series). University of North Texas Press. ISBN978-1-57441-262-8.
^Johnson, David; Parsons, Chuck (2008). John Ringo, King of the Cowboys: His Life and Times from the Hoo Doo War to Tombstone, Second Edition (A. C. Greene). University of North Texas Press. ISBN978-1-57441-243-7.