By 1900 the Zoo's size had increased to "about 170 acres" due to three successive additions on the park's southwestern edge bordering Cathedral Avenue. In fiscal 1921, the park acquired a long coveted 5-2/3 acre section of land in the present Connecticut Avenue entrance area, and in 1923 it purchased another 8,000 feet to protect the Adams Mill Road entrance. The next and most recent major boundary change was a loss of about ten acres in 1966 for Beach Drive. How ever, the deed for this land has not been changed, so officially the park's acreage remains 175 acres, although its real present size is 165 acres.
The present Zoo site was chosen because of its picturesque character its rugged terrain with numerous hills, and its location in Rock Creek Valley. While over the last half century many structures have been erected which impinge upon the landscape, the area still retains its rugged and green magnificence and the alternating views from the valleys and hills provide great visual excitement. The exhibition area is located in the northern half of the park and the southern portion is lightly built upon.
Bird House: Built 1928 (Howland Russell/A.L. Harris, architects)
Reptile House: Built 1931, (A.L. Harris, architect)
Small Mammal House: Built 1937 by Public Works Administration (Edwin H. Clarke, consulting architect)
Established 1889, expanded 1921, 1923; approximately 15 buildings 1892‑1940
DC listing November 8, 1964
National Register listing April 11, 1973