Zip Code: 21075
Location: 39.20 N, 76.75 W, which puts it at the eastern end of Howard County, Maryland.
About the name: Elkridge refers to the Elk Ridge, a line extending from Doughoregan Manor in the west to Oakland Mills in the south.
In 1608, John Smith (of Jamestown fame) traveled up the Patapsco River, and landed along the Elk Ridge. This landing was about as far up the river as anyone could navigate. No settlers came to the immediate area until 1687 when Lord Baltimore granted puritan Adam Shipley land close to the landing site. Eventually, a small dock was built at Elk Ridge Landing, which quickly became a convenient point for central Maryland farmers to ship hogsheads of tobacco.
Even though the landing was moderately busy from farm trade, the dock didn't really come into its own until the early to mid 1700s, when iron manufacturing became a big industry in the area. The port owes much of its success to Caleb Dorsey, who established the Elk Ridge Furnace in 1750. Dorsey's desire to ship his products to England helped grow the seaport to one of the busiest in the state.
In the 1830s construction began on the Thomas Viaduct, which would connect the Howard County side of the Patapsco River to the Baltimore County side. The viaduct was large enough to prevent destruction from flooding, and provided a permanent, nearby link for trade by rail to Baltimore.
Ground trade became much more important for the community as sea trade declined. A combination of factors led to the decline of the iron industry and the closure of the Elk Ridge Furnace in the late 1880s. Tobacco farms also began to decline as farmers focused on different crops. Meanwhile, as more people moved into the area and more farms began to develop, silt accumulated in the Patapsco and it became much harder for ships to navigate the river. It wasn't much longer before Elk Ridge Landing closed its docks, and the community simply became known as Elkridge, Maryland.
Elkridge Today: Modern Elkridge is actually a fairly small community, compared to other areas in Howard County. There are several historic sites that tourists come to visit, including the Elk Ridge Furnace and the Elk Ridge Tavern. It's still a very scenic area, and has been spared a lot of runaway development because of Patapsco Valley State Park, which runs alongside the town.
Information for this node taken from what I dimly remember from school, and from the Howard County website. Please /msg me if there is anything horribly incorrect here.