Ygnacio Nicanor Martínez (1774–1848) was a Californio politician, soldier, and ranchero, who served as the fourth Alcalde of San Francisco (then known as Yerba Buena).
He was an important figure in the development of Contra Costa and the city of Martinez, California is named after him.
In 1827, as a lieutenant stationed at the Presidio of San Francisco, Martínez met with the American explorer Jedediah Smith and helped to facilitate the continuation of Smith's northward travels toward the Columbia River.
Martínez married Maria Martina Arellanes in 1802, and the couple had eleven children: nine daughters and two sons.
Ygnacio Martínez died in June, 1848, in the area that would become Contra Costa County, and is buried at Mission San Jose Cemetery in Fremont, California.