I found the Johnston Family Tree, trees.ancestry.com/tree/18087419/person/603191365. Most larger libraries provide free access to Ancestry.com.
In 1900 the Johnston family was living in Loyal, Clark, Wisconsin.
Geo. W. Johnston, b. MN Feb 1869, engineer.
Martha, wife, b. England, March 1869, immigrated 1872.
Ruben R., b. MN June 1896.
On 1 June 1905 the family was living in Fenwood, Marathon, WI.
George W. Johnston, b. MN, 36,. day laborer.
Martha, wife, b. England, 36.
Reuben R., b. MN, 8.
Elwin J., b. WI, 2.
In 1910 the family was living in Wausau, Marathon, WI.
George W. Johnston, b. MN, 41, laborer ice & fuel co, marr 16 yrs.
Dorothy, wife, b. England, 41, had given birth to four children but only three alive in 1910.
Ruben R., b. MN, 13.
Elwin J., b. WI, 7.
Martha A., b. WI, 4.
In 1920 the family was living in Weston, Marathon, WI.
George E. Johnston, b. MN, 50, laborer.
Martha, b. England, 50.
Rubin, b. MN, 23.
Elwin J., b. WI, 17.
Martha, b. WI, 14.
Elwin J. Johnston
Born: 22 Aug 1902
Last Residence: Dallas, Polk, Oregon
Died: 1 Aug 1966
His retirement was from the Railroad Board and his retirement # was assigned 1951-1963.
Source: Social Security Death Index.
Thelma Amanda Johnston
Born: 5 Dec 1905
Died: 3 July 1989, Polk County
Death Cert #89-14327.
Source: Oregon Death Index 1898-2008.
Contact the Polk County Historical Society Museum, 503-623-6251 for copies of obituaries. Successful Searching!