Bryn Mawr (pronounced ; from Welsh for "big hill") is a census-designated place (CDP), located entirely in Lower Merion Township, Montgomery County, Pennsylvania, just west of Philadelphia along Lancaster Avenue (US-30) and the border with Delaware County.
There are also areas not in the census-designated place but which have "Bryn Mawr, Pennsylvania" postal addresses located in Radnor and Haverford Townships in Delaware County.
Bryn Mawr is located toward the center of what is known as the Main Line, a group of affluent Philadelphia suburban villages stretching from the city limits to Malvern. They became home to sprawling country estates belonging to Philadelphia's wealthiest families, and over the decades became a bastion of "old money". As of the 2010 census, it had a population of 3,779. Bryn Mawr is home to Bryn Mawr College.
Bryn Mawr is named after an estate near Dolgellau in Wales that belonged to Rowland Ellis. He was a Welsh Quaker who emigrated in 1686 to Pennsylvania from Dolgellau to escape religious persecution.
Until 1869 and the coming of the Pennsylvania Railroad's Main Line, the town, located in the old Welsh Tract, was known as Crankyville. The town was known as Humphreysville from 1800 to 1869 according to the Lower Merion Historical Society. The town was renamed by railroad agent William H. Wilson after he acquired on behalf of the railroad the 283 acres (1.15 km2) that now compose Bryn Mawr.
In 1893, the first hospital, Bryn Mawr Hospital, was built on the Main Line by Dr.