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America’s religious landscape has undergone remarkable transformations since the late 19th century. While browsing through historical records from the Association of Religious Data Archives (ARDA), I became fascinated by how different religious communities have shaped various regions of our country. This inspired me to create a series of maps visualizing these changes from 1890 to 2010.
Looking at the animated map above, we can see how immigration waves, urbanization, and social movements have influenced religious diversity across different counties. According to research from the Pew Research Center, the late 19th century saw dramatic increases in Catholic populations in northeastern cities, while Methodist and Baptist denominations expanded rapidly through the South and Midwest.
To create these visualizations, I used county-level data from ARDA and historical census records, applying Simpson’s Diversity Index to measure religious plurality. This scientific method calculates the probability of randomly selecting two people of different religious backgrounds in each county, using the formula D = 1 – ∑(n/N)², where n represents the number of people in each religious group and N represents the total population.
The 2010 map reveals some fascinating patterns. In the Northeast, cities like Boston and New York show remarkable religious diversity, reflecting centuries of immigration and cultural exchange. According to Harvard’s Pluralism Project, Boston alone hosts over 100 distinct religious communities, from historic Protestant churches to modern Buddhist temples.
The American South tells a different story. While many assume it’s uniformly Protestant, research from the Southern Studies Forum shows fascinating pockets of diversity. New Orleans, for instance, blends Catholic, Protestant, and Vodou traditions, while Atlanta has emerged as a center for various Protestant denominations and growing Jewish, Muslim, and Hindu communities.
The Midwest presents an intriguing mix of traditional and evolving religious patterns. The University of Minnesota’s Religious Studies Department has documented how Lutheran and Catholic settlements of the 19th century created lasting influences, while cities like Chicago and Minneapolis have developed into centers of religious innovation and interfaith dialogue.
Western states show perhaps the most dramatic changes over the past century. According to the Western Religious History Association, the region has transformed from having the lowest religious participation rates in the 1890s to becoming home to some of the most diverse religious communities in modern America.
