Simón G. Domínguez, school proprietor, salesman, and promoter of political unity of Texas Mexicans, lived in Laredo in the late nineteenth and early twentieth centuries. He married a woman named María, and they had four children. Domínguez was able to read and write in Spanish and English, and in 1908 he bought a typewriter. He founded and taught a private school or escuelita called Instituto Domínguez that operated from 1890 to at least 1913, with some interruption. María may have been a cofounder and teacher as well. Ninety-five students were enrolled in July 1911 and 150 in January 1912. The Instituto specialized in English and Spanish. It operated as both a day school for children and a night school for adults. The school had a telephone and may also have had a library with an encyclopedia. Domínguez also sold medicines, plants and seeds, and books that he obtained from companies across the United States. In 1904 he earned twenty-five dollars a month, with which he maintained a family of four.
He belonged to numerous sociedades mutualistas over several decades. In 1903 he belonged to the Sociedad Mutualista Hijos de Juárez, and in 1907 he was president. In 1912 he was a member of the Mexican Masonic lodge, the Knights of Pythias, the Woodmen of the World Lodge, and other minor lodges in Laredo. Around 1920 he was active in at least ten societies in Laredo. He corresponded with mutualistas in México, such as the Sociedad Mutualista Amigos del Trabajo and the Sociedad Unión de Jornaleros (Mutual-Aid Society of the Friends of Labor and Society of the Union of Day-Laborers).
As a delegate of the Hijos de Juárez, Domínguez addressed the first Congreso Mexicanista, the first known statewide political conference by la Raza (see RAZA UNIDA PARTY). In his speech on women's education, for which he was probably chosen because the Instituto permitted girls and women to enroll, he argued that education of women was indispensable not only for social position but also to mold the children.
Domínguez called for the merger of the six mutual-aid societies in Laredo, the merger of all sociedades mutualistas in the state, and the formation of a Congreso Masonico in each Texas town. He also proposed a night and day school of English and Spanish in each community, as he believed that both languages were needed for communication between Mexico and the United States. Domínguez also organized fiestas patrias. In 1910 he headed a commission to set up a Mexican Independence Centennial Celebration in Laredo and in 1914 helped initiate Cinco de Mayo. He was an acquaintance of the Idar family and may have written for La Crónica.