Ralph Dupuy Lacoe was born on November 12, 1824, in Pennsylvania, USA.

He was a self-taught paleontologist who lived in the small anthracite coal town of Pittston, Pennsylvania. Financially successful, he retired from his banking business in 1865 and devoted himself to full-time fossil collecting, amassing over 100,000 specimens that he donated to various repositories, e.g., the United States National Museum. He also employed collectors and procured many private collections. In the 1880s and the 1890s, a few of his reports were published by the Wyoming Historical and Geological Society.

In 1860, he married Bridget Clary (1831–1872). He died on February 5, 1901, in Pittston, Luzerne, Pennsylvania.