The Main Line region was long part of Lenapehoking, the homeland of the matrilineal Lenni Lenape Native Americans (the "true people", or "Delaware Indians"). Europeans arrived in the 1600s, after William Penn sold a tract of land, called the Welsh Tract, to a group of Welsh Quakers in London in 1681. This accounts for the many Welsh place names in the area.
The Pennsylvania Railroad built its main line during the early 19th century as part of the Main Line of Public Works that spanned Pennsylvania. Later in the century, the railroad, which owned much of the land surrounding the tracks, encouraged the development of this picturesque environment by building way stations along the portion of its track closest to Philadelphia. The benefits of what was touted as "healthy yet cultivated country living" attracted Philadelphia's social elite, many of whom had one house in the city and another larger "country home" on the Main Line.
In the 20th century, many of these families moved to the Main Line suburbs. Part of the national trend of suburbanization, this drove rapid investment, prosperity, and growth that turned the area into greater Philadelphia's most affluent and fashionable region. Estates with sweeping lawns and towering maples, the débutante balls and the Merion Cricket Club, which drew crowds of 25,000 spectators to its matches in the early 1900s, were the setting for the 1940 Grant/Hepburn/Stewart motion picture The Philadelphia Story.
The railroad placed stops about two minutes apart, starting with Overbrook. The surrounding communities became known by the railroad station names which started at Broad Street Station in Center City Philadelphia and went on to 32nd St. Station, and then the Main Line stations: Overbrook, Merion, Narberth, Wynnewood, Ardmore, Haverford, Bryn Mawr, Rosemont, Villanova, Radnor, St. Davids, Wayne, Strafford, Devon, Berwyn, Daylesford, and Paoli. At least five of these station buildings, along with the first Bryn Mawr Hotel, were designed by Wilson Brothers & Company. Broad Street Station was replaced with Suburban Station in 1930, and 30th Street Station replaced 32nd Street three years later. Suburban service now extends west of the Main Line to the communities of Malvern, Exton, Whitford, Downingtown, and Thorndale.
The railroad line then continued on to Chicago, with major stations at Lancaster, Harrisburg and Pittsburgh. The railroad, since taken over by Amtrak, is still in service, although its route is slightly different from the original. It also serves the Paoli/Thorndale Line of the SEPTA Regional Rail system.
Today, the "Main Line" is another name for the western suburbs of Philadelphia along Lancaster Avenue (U.S. Route 30) and the former Pennsylvania Railroad Main Line, extending from the city limits to, traditionally, Bryn Mawr and ultimately Paoli, an area of about 200 square miles (520 km2). The upper- and upper middle-class enclave has historically been one of the bastions of "old money" in the Northeast, along with places like Long Island's Gold Coast, Westchester County, New York, Middlesex County, Massachusetts, and Fairfield County, Connecticut. It is home to some of the wealthiest communities in the United States, such as Gladwyne, which has the 14th highest per-capita income in the country for places with a population of 1,000 or more. The eastern section of Villanova also was ranked 39th in "The Elite 100 Highest Income Neighborhoods in America" with a median annual household income of $366,904. Neighborhoods along the Main Line include nineteenth and early twentieth century railroad suburbs and post-war subdivisions, as well as a few surviving buildings from before the suburban area.
The Main Line proper is a line of communities extending northwest from the City of Philadelphia. From Philadelphia, the stations on what is now referred to as the Paoli/Thorndale (formerly "R5") Line are: Overbrook, Merion, Narberth, Wynnewood, Ardmore, Haverford and Bryn Mawr, which inspired the mnemonic "Old Maids Never Wed And Have Babies". The Main Line now encompasses many communities past Bryn Mawr including the Upper Main Line communities of Rosemont, Villanova, Radnor, St. Davids, Wayne, Strafford, Devon, Berwyn, Daylesford, Paoli, and Malvern.