The official boundaries of the City of Seattle Urban Center are Denny Way on the south, beyond which is Denny Triangle; Interstate 5 on the east, beyond which is Capitol Hill; Aurora Avenue N. (State Route 99) and 7th Avenue N. on the west, beyond which is Lower Queen Anne; and Galer Street, Lake Union, and E. Newton Place on the north, beyond which are Westlake and Eastlake,[3] but like most Seattle neighborhoods, its precise boundaries are indeterminate.

In particular Cornish College of the Arts and Vulcan Inc. properties such as 2200 and 2201 Westlake are officially in Denny Triangle for city planning and zoning purposes but often referred to as South Lake Union.

At the time, there were deer and elk in the area; natives also ate fish, clams, root vegetables, camas, bracken, wapato and berries.

Significant native settlement in South Lake Union lasted until 1875, when a windstorm knocked over a tree, destroying a longhouse in what is now Cascade.

At first, coal was transported from South Lake Union to the downtown docks by wagon, then from 1872 to about 1877 on a narrow-gauge railroad that followed the route of present-day Westlake Avenue to Pike Street.

[15] Meanwhile, the Northern Pacific Railway ran a railroad line around Lake Union and down Terry Avenue, where a freight station opened in 1913.

Cascade slowly lost its identity as a neighborhood distinct from the rest of South Lake Union, especially after construction of Interstate 5 cut it off from Capitol Hill.

[18] Microsoft co-founder Paul Allen donated $20 million to buy property for the Seattle Commons, which reverted to his ownership after the proposal was defeated by public votes in 1995 and 1996.

In April 2008, the new Lake Union Park opened to the public with a pedestrian bridge across the western waterway, a walkway along the waterfront, 1.6 acres (6,500 m2) of green space, landscaping and much more.

Vessels currently moored at the wharf include the steamer Virginia V,[20] the lightship Swiftsure, the tug Arthur Foss, the fireboat Duwamish, and the salmon troller Twilight.

[21] Opened in December 2012, the Museum of History & Industry relocated from Seattle's Montlake neighborhood to the former Naval Reserve Training Center, or "Armory.

The South Lake Union Campus of the University of Washington School of Medicine now includes 1250 people (researchers and staff) in four buildings.

The plan for development of a biotechnology hub in South Lake Union has been somewhat controversial, as it is seen by some as an example of influential private companies receiving benefits from the city.

In early Seattle history, South Lake Union had housing for both workers and owners of mills on Lake Union, including David Denny's residence at Dexter Ave N and Republican St.[27] By the 1960s, landowners including the Seattle Times demolished acres of housing for parking lots, leaving the Cascade Neighborhood as the only district with many residential options.

[28] As early as 1972, the mayor's "In-City Living Task Force" proposed the creation of 50,000 housing units in high-rise apartments in South Lake Union and Belltown.

In October 2012, Amazon announced it would spend over $1 billion to purchase its South Lake Union corporate headquarters from Microsoft co-founder Paul Allen's investment firm.