Yrjö Elfvengren (8 September 1889 – 10 June 1927) was a Finnish nobleman and white officer who was Chairman of the Provisional Committee of the unrecognized state of the Republic of North Ingria.

From 1911 to 1913, Georg Elfvengren served as a cornet in the Life Guard Cuirassier Regiment, based in Hatsina near St. Petersburg.

After the October Revolution in November 1917, on January 14, 1918, Elfvengren participated in a terrorist act against Lenin[clarification needed] along with other frontline officers.

However, a counterattack by the Soviet Russians forced them to retreat, and the North Ingrian Regiment withdrew back to Kirjasalo.

Upon Elfvengren's assumption of leadership, the relations between the interim committee of North Ingria and the Northwestern Army were strengthened.

In February 1920, under pressure from Finland, Elfvengren resigned from the chairmanship of the interim committee of North Ingria, after which he collaborated with the Commander-in-Chief of the White Army of South Russia, Pyotr Wrangel, and the Socialist Revolutionary Boris Savinkov.

In June 1921, together with Boris Savinkov, he established the Citizens' Union for the Protection of Fatherland and Freedom in Warsaw, aimed at overthrowing the Soviet government.

At the same time, 19 other individuals accused of counter-revolutionary activities were also executed in response to the assassination of Soviet diplomat Pyotr Voykov, including several members of Russian noble families.