Horace Whittier Peaslee, Jr. (November 9, 1884 – May 18, 1959) was an American architect and landscape designer who primarily practiced in Washington, D.C. Born in New York, he attended Cooper Union and the Cornell University College of Architecture, Art, and Planning before moving to the nation's capital to work for the United States Office of Public Buildings and Grounds.

During World War I, he served as a captain in the United States Army Corps of Engineers and designed some of the temporary buildings of the National Mall.

Peaslee opened his own architectural practice in the late 1910s and designed residential, religious, educational, and public properties during his career.

He was active in professional and social organizations, which included the Committee of 100 on the Federal City and National Capital Planning Commission, both of which he co-founded.

During his fellowship, Peaslee received an award from the Beaux Arts Society and his design of the Chatham Town Hall was chosen in a competition.

[5] In 1914, Peaslee and Burnap joined other officials from his office and members of the United States Commission of Fine Arts (CFA) on a tour of European gardens.

They visited France, Italy, Spain, and Switzerland, seeking inspiration for planned gardens and parks in the United States.

[2] During World War I, Peaslee served as a captain in the United States Army Corps of Engineers, designing some of the temporary buildings on the National Mall and barracks at Camp Humphreys in Fairfax County, Virginia.

Around this time Peaslee opened his own architectural practice in Washington, D.C. His designs and renovation works included residential, religious, educational, and public properties.

[19][20] In 1925, Peaslee designed a house for Colonel Clarence O. Sherrill at 2440 Kalorama Road NW in Sheridan-Kalorama, incorporating salvaged items from a demolished building.

[2][22] From 1931 to 1941, Peaslee worked with Greely and architect Harvey Baxter in designing Colony Hill, a planned community in Washington, D.C., consisting of a few dozen houses.

[16] The second was the Landon School, which had moved in 1936 from 2131 Massachusetts Avenue NW to an estate in Bethesda, Maryland, previously owned by socialite Evalyn Walsh McLean.

[30][31] Peaslee was one of five finalists in a competition to design the Tomb of the Unknown Soldier at Arlington National Cemetery, but architect Lorimer Rich was chosen in 1927.

[32] Peaslee and Nathan C. Wyeth served as associate architects on Frederick H. Brooke's design of the District of Columbia War Memorial, which was built on the National Mall in 1931.

Working with architect Fiske Kimball from 1928 to 1932, Peaslee's first major renovation project was the headquarters of the National Society of the Colonial Dames of America, which had purchased Dumbarton House in Georgetown.

[1][39] Around this time Peaslee also oversaw exterior and interior renovations of Belle Grove Plantation's manor house near Middletown, Virginia.

[47] Horace died from a heart attack the following year on May 18, shortly after receiving an award from the Washington Board of Trade for his work on the Episcopal Church Home (Bowie-Sevier House).

He lobbied for construction of the George Washington Memorial Parkway, passage of the Shipstead-Luce Act, and preservation of Great Falls when a proposal was made in the 1920s to build a power station on the Potomac River.