St. Mary's Parish Church located at what is now the corner of 15th and Stout streets was the first Catholic Church in Denver. Father Joseph P. Machebeuf celebrated the first Mass on Christmas eve of 1860. In 1868, Father Machebeuf was appointed as bishop of Colorado and St. Mary's became the Cathedral.
In 1890, Bishop Nicholas C. Matz built a brick and sandstone building at 1842 Logan Street. Its four floors were used as the Cathedral school and the basement was the pro-Cathedral or temporary Cathedral. John K. Mullen, John F. Campion, J.J. Brown and Dennis Sheedy paid for eight lots for the permanent Cathedral. In 1902, ground was broken for the new Cathedral. Work came to a halt due to a lack of funds caused by questionable investments made by the procathedral rector, Fr. Michael Callahan. In 1905, an energetic assistant, Hugh L. McMenamin or Father Mac, came to the Cathedral and organized fund raising efforts for the work to continue. The cornerstone was laid in 1906 and Father Mac was appointed rector of the Cathedral on July 26, 1908.
The twin 210 foot spires were capped in 1911. The exterior of the structure is made up of limestone from Indiana and granite from Gunnison, Colorado. The altar, statuary, and bishop's chair are all made of marble imported from Carrara, Italy.The seventy-five stained glass windows came from the F.X. Zetter's Royal Bavarian Institute of Munich. With the structure virtually complete, a bolt of lightning struck the west tower on August 7, 1912 and knocked off the top twenty five feet. The spire was repaired before the dedication. The total cost to build the Cathedral was approximately $500,000.
On October 27, 1912, the Cathedral of the Immaculate Conception was dedicated. Fifteen bishops and a cardinal, along with local dignitaries, attended the Mass. The following day, the Rocky Mountain News reported, "May the Cathedral of the Immaculate Conception long stand, its spires an expression of the questing, upturned face of humanity, its chimes an eternal call to the spirituality that stirs within us, and its doors a haven to the weary-hearted in search of hope and rest!" The Cathedral was consecrated in 1921 and elevated to a minor basilica on December 25, 1979. On August 13 and 14, 1993, His Holiness John Paul II celebrated Mass at the Cathedral as part of the World Youth Day celebration held in Denver that year. On June 23, 1997, the east spire of the Cathedral was struck by lightning. Repairs took nine months to complete. The east tower and spire were rededicated on June 23, 1998.
In the years that have followed, the Cathedral has remained a haven to Catholics and non-Catholics. Each week the Cathedral provides three daily Masses and five Sunday Masses to the faithful. Over half of those attending are visitors from other parishes and other cities. Each year the Cathedral provides 50,000 to 60,000 lunches to the poor and homeless. While the Cathedral is now an inner-city parish, its contributions to the community continue; and its financial needs are great.