In the 1870's, Denver had several railroad depots.  The station at 16th and Delgany was used by three railroads — sort of an early union station.  Denver's first railroad, the Kansas Pacific, used a station at 21st and Wazee, while the Denver Pacific's terminal was at the site of the present Denver Union Station. Toward the end of the decade, Financier Jay Gould organized the Union Depot & Railroad Company for the purpose of establishing a consolidated passenger terminal in the City.

Incorporated in 1879, the Union Depot Company began construction on a new terminal in 1880, and the facility opened for business by the middle of 1881 — a remarkably short time.  The completed building was 503 feet long and 65 feet wide. Stone for the building came from several different Colorado sites. Within a few years 60 trains arrived or departed from the station each day.  It had truly become the gateway to the Mile-high City.

On March 18, 1894, fire destroyed most of the depot. About a year later, the Union Depot was rebuilt within the existing exterior walls with a new clock tower, a lower profile roof and small dormers replacing the clerestory facade.

Traffic continued to grow, and by 1914 the station was deemed too small.  The center section of the old building was demolished and a new central waiting room built. Today, only the north and south wings exterior walls remain from the 1881 original building.

In conjuction with the 1914 addition, the Union Depot & Railroad Co. was reorganized as Denver Union Terminal Railway Company (DUTC) and the terminal itself renamed Denver Union Station. DUTC was owned by the railroads that served the station: Denver & Rio Grande, Chicago Rock Island & Pacific, Atchison Topeka & Santa Fe, Chicago Burlington & Quincy, Colorado & Southern, and Union Pacific.

Although there have been many changes to the building throughout the ensuing years, including the addition of the signature "UNION STATION  Travel by Train" sign in 1952, the station retains much of its original appearance. The historic site itself has remained open, but the parklike landscaping has been replaced by automobile parking lots.

While many millions of people have used the station since it opened in 1881, some of the more memorable include Presidents Harding, Taft, Hoover, Truman, Eisenhower and both Teddy and Franklin Delano Roosevelt.

Next year, Union Station will celebrate its 125th birthday. At the onset of the 21st century, Denver Union Station, newly incarnated as a multimodal transportation center, is on the threshold of a new era of greatness.