Dr. William R. Whitehead was the original owner of what is now know as the Whitehead/Peabody Mansion and the offices of Richard P. Arber Associates Consulting Engineers. He was born in 1831 to a wealthy and aristocratic family in Suffolk, Virginia. After studying medicine in the United States, he moved to Paris to study French and then moved to Vienna where he volunteered to serve as a surgeon in the Russian Army during the Crimean War. After spending numerous years in Europe, he settled in New York to continue his medical career. At the beginning of the Civil War, he returned to his true heritage in the South where he served as a surgeon in the Confederate Army. In 1872, following the Civil War, he moved to Denver due to his wife's poor health. He was able to quickly rise to be one of Denver's leading citizens. In 1874 be was elected to the Denver City Council. He soon became the chairman of the Denver Board of Health. In addition to his social and political prominence, Dr. Whitehead was also an early leader of Denver's medical community. He published numerous medical journals, and in 1877, he was elected President of the Denver Medical Association. By 1889, when he commissioned the construction of his house on Grant, he was a well established Denver citizen. By the time he lived on Grant he was in retirement until his death in 1902.

James H. Peabody, a Republican businessman from Canon City, was elected Governor of Colorado in 1903. At this time, Colorado did not have an official Governor's mansion, so Peabody set out to find a residence in Denver. Peabody took residence in 1128 Grant during his term in office; however was only known to live there during 1903 and 1904. As Governor, Peabody played a pivotal role in the violent clash between forces for and against unionization of Colorado's miners. "Peabodyism" became the principle issue in the 1904 election between Peabody and Alva Adams, who had served two previous terms. Adams won the election and was inaugurated, but political intrigue resulted in the Republican legislature declaring that Peabody had won. Peabody served one day before resigning on March 17, 1905 to be succeeded by Lieutenant Governor Jesse F. McDonald.

Frank E. Edbrooke built the Whitehead/Peabody Mansion in 1889. Edbrooke is also known for the Brown Palace Hotel, the Central Presbyterian Church, the Tabor Opera House, and the Sisters of Loretto Academy. His architectural stature has resulted in a recent revival of sorts of his popularity and the naming of a newly renovated projects in Lower Downtown in his honor. The house itself is architecturally noteworthy. Its design is robust but clean in proportion and detail, and is representative of an important progressive sensibility for its time in its similarity to the contemporary Arts and Crafts Movement. The architecture of the house employs the massive masonry walls and chimneys and steeply pitched roof of an English county house. It has a generous porch and formally organized facade that address the street. The front wall is subtly articulated with a tall, narrow slot and a flat arch in the brick work. Edbrooke was commissioned to do the house by one of Denver's early leaders, which was later occupied by one of Colorado's most controversial Governors.