Aside from farming, Irmo's very first industry was the Piedmont Land Improvement Company. The CN&L railroad obtained much of the lumber for the trestle woodwork. The first train service through Irmo began in July, 1890.

The location of Irmo was selected because a site approximately 10 miles from Columbia was needed for refueling of the wood-burning locomotives and water replenishment. The CN&L railroad chose the site of IRMO to be the refueling site and the name was formed by combining the first two letters of Captian C.J. Iredell (Secretary-Treasurer of the CN&L) and H.C. Moseley (President of the investment company and also the first president of the CN&L railroad). There is no record of the names (if any) that were rejected.

Irmo was originally one square mile in area, but annexation has vastly increased the town limits during the last 25 years. 

In February 1927, a water company in Lexington submitted a permit request to build a mile-and-a-half long earthen dam on the Saluda River. It was to be the the largest earthen dam in the world. . . no small endeavor. It would create a lake over 40 miles long and about 14 miles wide (78 square miles). It would flood over 50,000 acres and hold almost 800 billion gallons of water. The application was granted on July 8, 1927. The developers had to obtain over 1,100 different parcels of land that had over 5,000 people living on it (aproximately 100,000 acres). Six schools, three churches, and 193 graveyards containing 2,323 graves were relocated to flood-free zones. Many other graves remain under the lake. Markers at Bethel Lutheran Church in White Rock and St. Michael's Lutheran Church on River Road bear the names of family members whose graves still lie at the lake-covered site of the original High Hill cemetery.

A large percentage of the land was covered by timber and supplied all of the lumber needs for the project. Thirty-seven sawmills were born with 2,000 employees that manufactured over 100 million board feet of lumber. All told, over 4,000 people were employed in the raising of the history making dam.

The first load of dirt was dumped on the site on September 21, 1927 and the last load of dirt was dumped on June 28, 1930. The dam covers 99 acres, 208 feet high and is 1,150 feet in width at the bottom, and 25 feet wide at the top. The intake towers required more than 636,000 bags of cement, 122,000 tons of stone and gravel, 62,000 tons of sand and almost 4,000 tons of steel plate.

The lake began filling on August 31, 1929 and reached the elevation of 290 feet by April of 1930. One woman who refused to move out of her house boasted that she could drink the water faster than it could rise. She was rescued as the lake level reached her house and eventually covered it up.

The name of Lake Murray was given in honor of William Spencer Murray of the Murray and Flood firm of New York City, designers of the project.