In 1791, President George Washington determined that the survey to establish the boundaries of the ten-mile-square Federal District should begin at Jones Point, south of Alexandria, and should proceed northwestward so as to exclude the Falls Church. The survey was made that summer, and boundary stones were set up at one-mile intervals. The District of Columbia was not organized until 1801, however. The part of Fairfax County ceded by Virginia to federal jurisdiction was then organized as Alexandria County, which included the Town of Alexandria. All of the present Arlington County was located in the original Ten Mile Square of the District of Columbia.

The population of the new county in 1800 was not quite 6,000, of whom some 5,000 lived in the town of Alexandria and only 978 in the rural area. There were 297 slaves in the country part and 875 in the town of Alexandria.

The first bridge across the Potomac was built by the merchants of Georgetown in 1797 near the site of the Falls Warehouse. It was intended to draw the trade of the Leesburg area away from Alexandria to Georgetown. The response of the merchants of Alexandria was the opening of the Leesburg Turnpike (now Leesburg Pike, State Route 7). After the Falls Bridge had been twice carried away by floods, the merchants of Georgetown built there, in 1808, a high chain suspension bridge that was considered a marvel of engineering at that time. So famous was the name Chain Bridge that it has remained the name of the bridge over the Potomac although the chain suspension was replaced by a steel suspension bridge in 1853.

The merchants of Washington had the Long Bridge built in 1808 in the present location of the railroad bridge parallel to the two spans that carry US-1 and I-395. From it, the Columbian Turnpike (Columbia Pike, State Route 244) was built westward to intercept the Leesburg Turnpike and the Little River Turnpike (State Route 236). Another turnpike was built from the Long Bridge to Alexandria; it is now the Jefferson Davis Highway (US-1). In 1809, the Georgetown and Alexandria Turnpike was chartered, crossing Custis family lands; a portion of it is now Arlington Ridge Road.

Ellicott’s 1793 map showing the Arlington portion of the 10-mile square of the District of Columbia.

Attempts to increase trade with the west prompted various canal projects. In the 18th century, George Washington and other prominent leaders established the Patowmack Canal Company with the hope of drawing trade to Alexandria. Although this project failed, efforts persisted to build a waterway. In 1828 ground was broken for the Chesapeake and Ohio Canal Company. This canal company was established to construct and operate a canal along the north shore of the Potomac from tidewater westward.

The Alexandrians foresaw that this canal would bring the trade of the upper country to Georgetown and Washington; they demanded a terminus at Alexandria. To this end they formed the Alexandria Canal Company and built the Aqueduct Bridge and Alexandria Canal, 1833- 1843. The work proved more costly than had been anticipated; federal support for it was meager. At the same time the Commonwealth of Virginia was engaged in an extensive program of such public works. The Alexandrians appealed to Richmond for help. The obvious answer was that Virginia could not subsidize a canal project in the District of Columbia. The Alexandrians thereupon petitioned Congress for retrocession to Virginia.

Congress was willing, believing that the federal government would never have any need for land and jurisdiction in Alexandria County. In 1846 the County voted in favor of retrocession, and in 1847 the retrocession was accomplished. Instead of returning the area to Fairfax County, Virginia, Alexandria County remained a separate county. At the time of retrocession, the population of Alexandria County was 10,000, of whom 8,700 lived in the town of Alexandria and 1,300 in the rural area.