The Capitol Hill neighborhood is located in the shadow of the Capitol. The extent of the shadow is subject to question, but for the purposes of this guidebook, the neighborhood encompasses the area beyond the Capitol and the institutional buildings that make up the Capitol Complex and extends east and south to the Anacostia River. The northern boundary is Florida Avenue, marking the northernmost extent of the L'Enfant City. The later extension of Benning Road to the Anacostia River completes the northern boundary. With the exception of an unrealized cathedral fronted by a great plaza five blocks south of the Capitol, the public spaces planned by L'Enfant exist nearly in the form he intended.

Within this area are block after block of low-rise town houses, row houses, and a few apartment houses. Punctuating this remarkable homogeneity are school buildings, firehouses, churches, and occasional commercial structures. Slicing through the neighborhood are the major commercial thoroughfares of Pennsylvania Avenue SE, Eighth Street SE, and H Street NE. Ringing the area's borders are large public installations. On the south is the sprawling Navy Yard, a major employment center on the Anacostia River. Institutions such as the District Jail complex, D.C. General Hospital, the D.C. National Guard Armory, the Robert F. Kennedy Stadium, and parklands are located along the eastern boundary of the neighborhood.

While the neighborhood derives its name from its proximity to the Capitol, it actually is not located on a hill. The Capitol is situated on the highest point of land between the Anacostia and Potomac rivers, hence its name Capitol Hill. The Capitol Hill neighborhood developed on the high plateau extending east from the crest of the hill.

The deep waters of the Anacostia River south and east of the area appealed to the city's early planners. L'Enfant suggested that the shoreline be devoted to major port facilities, which, in turn, would generate commercial activities. East Capitol Street, running due east from the Capitol to the Anacostia River, was to be 160 feet wide. Along this major axis, “shops will be most conveniently and agreeably situated.” Midway along East Capitol Street, on the site of Lincoln Park, was to be a “historic column, from whose station, (a mile from the Federal house) all distances of places through the Continent, are to be calculated.” 42Present-day Lincoln Square on East Capitol Street, midway between the Capitol and the Anacostia River, is in the form and location originally planned. It was the outer boundary of the residential neighborhood in 1876, when Thomas Ball's Emancipation Monument was erected solely from the contributions of freed slaves.

From the area's northern boundary, roads led to Bladensburg, Maryland, then a thriving commercial port along the Anacostia. Public reservations or parks are placed at intersections of major diagonal streets that emanate from the Capitol with other diagonal thoroughfares. Several of these parks gave names to their immediate surroundings, such as Stanton Park, Lincoln Park, and Seward Square.

L'Enfant's expectations for a commercial East Capitol Street did not materialize, but his growth plan for the city and for the area known today as the Capitol Hill neighborhood did. The Capitol and the Navy Yard (see CN45) served as two major nodes of growth, while the public parks and the Eastern Market (see CN33) generated their own modest settlements. By the mid-nineteenth century, the Capitol Hill neighborhood was densely settled in a fiveblock radius around the Capitol and a radius of nearly equal size around the Navy Yard.

During the early years of the city, boardinghouses near the Capitol housed members of Congress. Laborers who were employed in the construction of the Capitol lived in shanties and barracks. Frame and brick houses were erected for the skilled workers and supervisors. In lands beyond, freestanding houses surrounded by extensive grounds were constructed. After the Civil War, substantial brick town and row houses were constructed to appeal to the increased rolls of middle-class civil servants. They made their homes in these two- and three-story houses, many of which followed a predictable design of a side entrance and a projecting bay window. Terracotta, pressed brick, stone trim, and cast-iron railings and stairs adorned these houses.

Urban development along the Anacostia River caused siltation and created marshy areas. The waterway's role as the site of deep-water ports was precluded. The McMillan Plan of 1901–1902 recommended that the river's edges be reclaimed for much-needed parkland in the eastern section of the city. The Army Corps of Engineers accomplished this work during the 1920s and 1930s, providing for large expanses of parklands on both sides of the river. By then, row house development had reached nearly to the river's edge.

In 1929, the National Capital Park and Planning Commission resurrected L'Enfant's idea of East Capitol Street as a major axis. Instead of a commercial thoroughfare, the planning commission produced a scheme for an East Capitol Street mall of public and semipublic buildings terminating at the Anacostia River in a sports center. In keeping with that plan, the headquarters of several states are located along the street. With this scheme, the planning commission hoped to relieve traffic congestion west of the Capitol. The plan's appeal endured for decades, and as late as the early 1960s East Capitol Street was designated part of a network of “special streets and places.”

By the mid-twentieth century, many middle-class families had left Capitol Hill and the area had deteriorated. Studies of blighted and obsolete areas of the District depicted large sections of the Capitol Hill neighborhood as ripe for urban redevelopment. Fortunately for the historic character of Capitol Hill, the Southwest Quadrant was given higher priority. In the meantime, the charm of the older buildings attracted a new group of affluent residents to the area. Starting in the 1950s, the restoration of Capitol Hill gradually gentrified housing closest to the Capitol and then proceeded to outlying blocks of older town and row houses, displacing lower- and lower-middle-class residents. Today, a large swath of Capitol Hill falls within the Capitol Hill Historic District. Much of Capitol Hill, both within and outside the historic district, looks much as it did in the early twentieth century, a testament not only to private preservation efforts but also to lesser development pressures when compared with the forces that overtook areas to the west of the Capitol.

The Capitol Hill Historic District is the largest residential historic district in the city, embracing over 150 city blocks. Its boundary is an irregular rectangle, generally running east from the Capitol Complex to 14th Street, north to F Street, and south to the Southeast Expressway. Its construction history spans that of the Capitol Hill neighborhood, from its founding in the L'Enfant Plan of 1791 to recent infill construction. However, the greatest concentration of buildings dates from the post-Civil War era. Many of the earlier buildings were demolished or greatly altered, and the twentieth-century buildings made modest and compatible contributions to a character that was already well formed.

One of the distinctive aspects of the historic district is the street pattern. L'Enfant specified that the diagonal avenues and principal streets, such as East Capitol Street, be 160 feet wide while the remaining grid streets be 90 feet wide. These dimensions have been achieved not through the width of the thoroughfares alone but also through the use of green space, the open space or front yards of each house. Thus, on East Capitol Street, the building line is set far back from the street curb, creating a privately maintained strip of green carpet that stretches from the Capitol grounds to the D.C. National Guard Armory, punctuated midway by Lincoln Park. The narrower grid streets provide for narrower green front yards for the rows of houses.

Development on Capitol Hill occurred piecemeal, involving many single houses set close to their neighbors and larger groups of houses with common-party walls. Because of the fragmented nature of construction, houses and groups of houses were scattered throughout a large area, with later houses constructed to fill in empty lots. The row and town houses bordering the streets range from one-of-a-kind, large, three-story brick and stone houses standing adjacent to two-story frame structures and groups of identical modest brick row houses. The greatest number of houses were developed during the last three decades of the nineteenth century and are Queen Anne and Romanesque Revival in style. While architects designed many of these houses, contractors and builders played a significant role in producing fairly standardized houses that met the taste and income level of the middle-income civil servants. In the Navy Yard and Marine Barracks area, the houses tended to be more modest because they accommodated blue-collar workers. In addition, the concentration of the black population in blocks in the Southeast Quadrant from the Capitol east to 11th Street also resulted in a more modest scale of housing in the Navy Yard–Marine Barracks area.

The row houses of the 1880s and 1890s were in part products of the District's building regulations that allowed for projecting bay windows. These houses were adorned with heavy window lintels of stone or cast iron, rows of decorative pressed brick and terracotta, stained-glass windows, decorative cast-iron staircases and railings, and heavily rusticated stone foundations. The variety of decorative treatments within a limited range of scale and material resulted in both the variety and the consistency that give the Capitol Hill Historic District its special character.