Entry in progress—B.P.
 
Wikipedia: Capitol Hill, Washington, D.C.
Capitol Hill, aside from being a metonym for the United States Congress, is the largest historic residential neighborhood in Washington D.C., stretching easterly in front of the United States Capitol along wide avenues. It is one of the oldest residential communities in Washington, and with roughly 35,000 people in just under two square miles, it is also one of the most densely populated.
 
As a geographic feature, Capitol Hill rises in the center of the District of Columbia and extends eastward. Pierre L’Enfant, as he began to develop his plan for the new Federal City in 1791, chose to locate the “Congress House” on the crest of the hill, facing the city, a site that L’Enfant characterized as a “pedestal waiting for a monument.”
 
The Capitol Hill neighborhood today straddles two quadrants of the city, Southeast and Northeast, and a large portion is now designated as the Capitol Hill historic district. The name Capitol Hill is often used to refer to both the historic district and to the larger neighborhood around it. To the east of Capitol Hill lies the Anacostia River, to the north is the H Street corridor, to the south are the Southeast/Southwest Freeway and the Washington Navy Yard, and to the west are the National Mall and the city’s central business district.
 
History
L’Enfant referred to the hill chosen as the site of the future Congress House as “Jenkins Hill” or “Jenkins Heights.” However, the tract of land had for many years belonged to the Carroll family and was noted in their records of ownership as “New Troy.” While it was rumored that a man named Jenkins had once pastured some livestock at the site of the Capitol (and thus his name was associated with the site), artist John Trumbull, who would paint several murals inside the Capitol’s rotunda, reported in 1791 that the site was covered with a thick wood, making it an unlikely place for livestock to graze. Who Jenkins was and how his name became associated with the hill, as reported by L’Enfant, remain unclear.[1]
 
The neighborhood that is now called Capitol Hill started to develop when the government began work at two locations, the Capitol and the Washington Navy Yard. It became a distinct community between 1799 and 1810 as the federal government became a major employer. The first stage in its early history was that of a boarding house community developed for members of Congress. In the early years of the Republic, few Congressmen wished to establish permanent residence in the city. Instead, most preferred to live in boarding houses within walking distance of the Capitol.
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Description
Capitol Hill’s landmarks include not only the United States Capitol, but also the Senate and House office buildings, the Supreme Court building, the Library of Congress, the Marine Barracks, the Washington Navy Yard, and Congressional Cemetery.
 
It is, however, largely a residential neighborhood composed predominantly of rowhouses of different stylistic varieties and periods. Side by side exist early 19th century manor houses, Federal townhouses, small frame dwellings, ornate Italianate bracketed houses and the late 19th century press brick rowhouses with their often whimsical decorative elements combining Richardsonian Romanesque, Queen Anne, and Eastlakian motifs.
 
The main non-residential corridor of Capitol Hill is Pennsylvania Avenue, a lively commercial street with shops, restaurants and bars. Eastern Market is an 1873 public market on 7th Street SE, where vendors sell fresh meat and produce in indoor stalls and at outdoor farmers’ stands. It is also the site of an outdoor flea market every weekend. After a major fire gutted the main market building on April 30, 2007, it underwent restoration and reopened on June 26, 2009.
 
The Hiram W. Johnson House, a National Historic Landmark located on Capitol HillBarracks Row (8th Street SE), so called because of its proximity to the U.S. Marine Barracks, is one of the city’s oldest commercial corridors. It dates to the late 18th century and has recently been revitalized.
 
Recent estimates in Capitol Hill newspapers suggest as many as a third of all Members of Congress live on Capitol Hill while in Washington
   
The Free Dictionary
Capitol Hill
n. Informal
The U.S. Congress.
 
Merriam Webster’s Online Dictionary
Main Entry: Capitol Hill
Function: noun
Etymology: Capitol Hill, Washington, site of the United States Capitol
Date: 1935
: the legislative branch of the United States government
 
OCLC WorldCat record
Part of the city of Washington shewing the heights of the present surface of the ground from Pennsylvania Avenue to New Jersey Avenue below the Capitol Hill
Author: Rt King
Publisher: [1803?]
Series: [Peter Force map collection, 777] 
Edition/Format: Map : Manuscript : English
 
OCLC WorldCat record
Message from the president of the United States, relative to such leases or contracts as may have been agreed upon and entered into between him and the owners of the new building on the Capitol Hill, for the use and accommodation of Congress. (Pursuant to a resolution of the Senate, of the 4th instant.) : February 15, 1822. Printed by order of the Senate of the United States.
Author: James Monroe; John Quincy Adams; United States. Dept. of State.; United States. President (1817-1825 : Monroe).; United States. Congress Senate.; All authors
Publisher: Washington [D.C.]: : Printed by Gales & Seaton., 1822.
Series: Senate document (United States. Congress. Senate), 17th Congress, 1st session, no. 21. 
Edition/Format: Book : National government publication : English
 
OCLC WorldCat record
John Underwood’s Journal : Capitol Hill, Washington City, 1855-1856.
Author: John Ingle Underwood
Edition/Format: Book : Manuscript : English
Summary: Journal kept by a John Ingle Underwood, of “Kirkman near Dunkirk, N.Y.,” containing entries for each day. Topics concern school courses, church attendance (various denominations, primarily Presbyterian), missionary meetings, lectures at the Smithsonian, various accounts for expenditures, etc. Entries after May 7th, 1855 are primarily written in shorthand, probably Taylor’s shorthand, since Mr. Underwood mentions the purchase of “Taylors short hand book” on Jan. 13th. Also includes an autograph manuscript of a song (without music) by Underwood entitled, “Apostrophe to the Flag” (3 leaves laid in), which includes 2 copies of the first page.
 
Google Books
Safire’s Political Dictionary
By William Safire
New York, NY: Oxford University Press
2008
Pg. 316:
Hill, the Capitol Hill, location of the House and Senate; familiar term for the legislative branch of U.S. government, as White House is for the executive branch.
 
“On the Hill” is frequently used in roundups of news from Washington, D.C.; White House aides for legislative liaison take messages “up to the Hill.”