Jacob L. Larmour, architect, was born in Hackensack, New Jersey, on June 26, 1822. He practiced architecture until 1857 in New York City and then moved his family to Jackson, Mississippi. The 1860 census of Jackson lists "J. Lamour" as an architect with family members including his wife, E. B., and children, M. T., J. M., and K. He served as an officer in the Confederate Army. After the war the family moved to Indianapolis, Indiana, and then to Minneapolis, Minnesota.
In 1871 Larmour moved to Austin, Texas, with his family. Austin was experiencing rapid growth after its designation as the permanent state capital in 1870. With the end of Reconstruction in 1872, new investments were initiated by public and private interests. Larmour exerted a substantial influence on the construction industry that molded Austin's built environment and established himself as one of the most prominent architects in nineteenth-century Texas. He was the only architect listed in the first Austin City Directory (1872–73). He immediately began work for the state of Texas by designing the Main Building at the Agricultural and Mechanical College of Texas (1871–74, burned 1912). His work for the state continued throughout his career, and he was appointed state architect in 1879 by Governor Oran M. Roberts and state architect of the penitentiaries in 1883. Between 1870 and his retirement in 1900 Larmour had various partners: Charles W. Wheelock in 1875, E. H. Klerke in 1876, W. W. Larmour (later of Waco) and Alphus Larmour in 1879, James Wahrenburger in 1879 (in San Antonio), Arthur O. Watson in 1886, and Dennis R. Walsh in 1898. Larmour and his offices produced more than fifty documented public, commercial, and residential buildings in Texas. His designs exhibited the range of high-style architectural elements characteristic of the times. He was a charter member of the Texas State Association of Architects, organized in 1886.
In Austin he designed additions to the Blind Asylum (see TEXAS SCHOOL FOR THE BLIND), the State Lunatic Asylum (1875, later known as Austin State Hospital), and the Texas School for the Deaf (1876). His work contributed substantially to the transformation of Congress Avenue. Larmour and Wheelock designed the First National Bank (1873), the Travis County Courthouse (1875, demolished 1964) at the southeast corner of Congress and Eleventh, and the Travis County Jail and Jailer's House at Brazos and Eleventh streets (with E. H. Klerke, 1875); and commercial buildings at 902–918 Congress (1875–76), Brueggerhoff's store (ca. 1887) at Congress and Tenth, the John Orr Building (also known as the Austin Board of Trade Building, 1889) at Congress and Sixth, and City National Bank (1891). In other areas of the state he is credited with the Texas State Penitentiary at Huntsville (1879), the Val Verde County Jail and Courthouse (1885–87), the Milam County Courthouse (1890–91), the Comanche County Courthouse (1890), the Llano County Courthouse (1890), the Grimes County Courthouse (c. 1891, burned), the Southwest Lunatic Asylum, San Antonio (1899), and buildings at Prairie View A&M (1899).
Larmour married Elizabeth B. Winant in 1844. They had one son and two daughters. Their son, later an architect in Cleveland, Ohio, evidently did not accompany the family to Texas. Larmour lived at 1909 Whitis in Austin. His Victorian L-plan cottage (ca. 1875) was moved to 1722 Rio Grande in 1980 and rehabilitated as office space. Elizabeth Larmour died in Austin on March 28, 1897, of pneumonia, and Jacob Larmour died in Austin on November 9, 1901. They were members of St. David's Episcopal Church.