The Mid-Atlantic Region

The Census Bureau calls this division Middle Atlantic, and it contains three states: New York, New Jersey and Pennsylvania. That is the whole list. It is a division inside the Northeast region, not a region of its own, and it is narrower than the Mid-Atlantic most Americans picture, which usually stretches south to take in Delaware, Maryland, the District of Columbia and often Virginia. The Census Bureau files all of those in the South.

The three Middle Atlantic states

State	Capital	Largest city	Statehood
New York	Albany	New York City	1788
New Jersey	Trenton	Newark	1787
Pennsylvania	Harrisburg	Philadelphia	1787

All three were among the original thirteen, so the years above are their ratification of the Constitution rather than admission: Pennsylvania on 12 December 1787, New Jersey on 18 December 1787, New York on 26 July 1788. None of the three has its largest city as its capital, a split shared by only a handful of states.

Population, land and economic weight

The 2020 Census counted 42,492,943 people across the three states, 12.8 percent of the country, on 99,223 square miles, 2.8 percent of the land. That is 428 people per square mile against a national figure near 94. The division holds 74 percent of the Northeast's population. New Jersey is the most densely populated state in the country; New York runs the third largest state economy after California and Texas, and Pennsylvania is close behind in the national top ten. The three carry 61 electoral votes, and New York and Pennsylvania each lost a House seat in the reapportionment following the 2020 Census.

The geography that made the corridor

The three states stack four landform belts from the coast inland: the Atlantic Coastal Plain across southern New Jersey, the Piedmont, the folded Ridge and Valley of central Pennsylvania, and the Allegheny Plateau. The Fall Line, where Piedmont rock drops to soft coastal sediment and rivers stop being navigable, fixed the sites of Trenton and Philadelphia. The Adirondacks of northern New York are not Appalachian at all; they are an uplifted dome of Canadian Shield rock.

The decisive feature is a gap. The Hudson and Mohawk valleys form the only near sea level break through the Appalachian wall between Alabama and the St. Lawrence. That gap is why the Erie Canal could be dug at all, and why New York rather than Philadelphia became the country's commercial capital after 1825. Water otherwise runs off in three directions: the Delaware and the Susquehanna to the Atlantic and the Chesapeake, the Allegheny and Monongahela joining at Pittsburgh to start the Ohio, and Lake Erie and Lake Ontario draining north through Niagara Falls.

How the middle colonies were settled

None of the three began as English. The Dutch planted New Netherland on Manhattan in 1624 and held it until England took it in 1664 and renamed it New York. Sweden held a colony on the lower Delaware from 1638. William Penn received his charter in 1681 and made religious tolerance the founding policy, which drew German sects, the Pennsylvania Dutch, and Scots-Irish who then pushed down the Appalachian valleys into the South. The middle colonies were the plural ones from the start, with no single established church and mixed grain farming rather than plantations.

Philadelphia housed the Continental Congress and the Constitutional Convention of 1787, and served as the national capital from 1790 to 1800. Gettysburg was fought in southern Pennsylvania in July 1863. Ellis Island, in New York Harbor, processed roughly twelve million arrivals between 1892 and 1954.

What the region is known for

The New York Stock Exchange and Nasdaq both sit in Manhattan, the largest city in the country. Philadelphia is the sixth largest. New Jersey holds a dense pharmaceutical corridor, Pennsylvania built its wealth on anthracite in the northeast and bituminous coal and steel around Pittsburgh and Bethlehem, and the Marcellus Shale has since made it the second largest natural gas producing state after Texas. The Northeast Corridor rail line links Philadelphia, Trenton, Newark and New York on the busiest passenger route in the United States. Five presidents were born in New York, two in Pennsylvania and one in New Jersey.

Where the boundary is argued

Almost everyone draws this one wider than the census does. Ask where the Mid-Atlantic ends and most people say the Mason-Dixon Line, surveyed between 1763 and 1767 by Charles Mason and Jeremiah Dixon to settle a boundary quarrel between the Penn and Calvert families, which would put Maryland and Delaware south of it. Yet Delaware and Maryland were middle colonies by every colonial measure, and Delaware ratified the Constitution first. Internally the division argues with itself: upstate New York has little in common with New York City, and Pittsburgh sits west of the Appalachian divide and is often called Midwestern by people who live there.

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