If you read The Banner’s data work, you know the Black Butterfly — the majority Black area of Baltimore. You may not know, though, that it’s gotten smaller. The landmass known as the Black Butterfly shrunk, just slightly, for the first time in 2020, while becoming more prominent in Baltimore County.

We’ve written a fair bit about the Black Butterfly here at The Banner. It’s appeared repeatedly in our data stories, and we recently published a roundup of different datasets where we’ve found it.

But, today, we’re showing how it changed over the years, and how it’s starting to extend to Baltimore County.

To do this, we’re using data from every decennial Census since 1940, and looking in both Baltimore City and Baltimore County.

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Press the “play” button on the chart below to see the change:

You can already see the Black Butterfly in 1940. It was smaller then than now — reaching only to Mondawmin in the west and Belair-Edison in the east — but still clearly visible.

Even the beginnings of the White L appear, with downtown having a smaller percentage of Black residents than the areas around it. At the time, The Evening Sun called this area the Black Archipelago, using an outdated and offensive word to refer to Black Americans.

From 1950 to 1970, the Butterfly takes on its modern shape, going from the same, small area in 1950 as 1940, to reaching the city border on the west in 1970.

It’s worth mentioning, though, that while the west wing of the Butterfly reached the border in 1970, at that time the east wing was still a few miles away from the county. Even today, the Butterfly is left-handed. In the west, most census tracts are 90 to 100% Black, while areas in the east of the city are mostly between 60 and 90% Black.

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Demographic trends, however, don’t respect jurisdictional lines, and in the last few decades the Black Butterfly has crossed into Baltimore County.

Press the “play” button on the chart below to see the Butterfly move into the county.

This change is relatively recent. The first majority-Black Census tract in Baltimore County appears in the 1980 Census. But, even then, the left-handedness of the Butterfly is apparent.

From 1970 to 2010, majority-Black Census tracts spread from the city, through Baltimore County, until they reach all the way to the county’s western border with Howard and Carroll counties. There’s almost no expansion of Black tracts from the right wing of the Butterfly in the city during that time.

I’ve previously called the majority-Black area just outside the western city line the “blue horn,” for its Democratic voting preference, but it’s better described as a lopsided Butterfly. Between 2010 and 2020, the majority-Black tracts very clearly start moving from the eastern part of the city over the county line and into White Marsh and Middle River.

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In the 1940s, The Evening Sun also noted that Black residents in the city were concentrated into tight geographic areas. Douglas Massey, sociologist at Princeton University, attributes this segregation to the deed restrictions, racial covenants and redlining that were prevalent in Baltimore.

That’s clearly true. In this chart, the solid orange line (the Black population of Baltimore City) is far above the dashed orange line (the landmass of Baltimore City that is majority-Black) during the 20th century. The gap, though, closes sharply after 2000, getting pretty close to 0 in 2020.

Baltimore County, however, sees the exact opposite trend. Its Black residents are more tightly concentrated today than they were in ’90s, and, shockingly, more concentrated than the city under racial covenants.


Nick Thieme designs statistical experiments and analyzes data to discover and improve stories about inequality, human rights, health care, and climate change. He has worked as a data reporter and statistician for a variety of public and private organizations, with writing appearing in the Atlanta Journal-Constitution, Slate Magazine, and elsewhere.

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