US Religion by County, 1950 Census

[RI]

The last time the US Census asked about religion:

Image Link

[RI]

Trying to zoom in on NYC, I'm assuming Jewish is the plurality in the Bronx and Brooklyn?

Yes, Jewish is the plurality in Bronx, Kings, and Sullivan counties in NY, plus Miami-Dade in FL. Manhattan was pretty close to a Jewish plurality (36%), but not quite there. Queens was 1/3 Jewish.

[RI]

NYC had about 2 million Jews in the 1950s and the Bronx and Brooklyn were clearly the "Jewish boroughs" then.  There's no way Manhattan was 36% Jewish at the time. 

Queens did see rapid Jewish growth in the 1940s and 1950s.  As late as 1940, Queens was more German/Irish/"old stock American" than it was Jewish/Italian. 

My understanding is that they didn't directly ask about the Jewish population in 1950, but instead tried to estimate it (for obvious reasons). The rest of their numbers look pretty good, so I'm not sure why they'd overestimate the Jewish population in Manhattan and Queens.

[RI]

Here's a comparable map from the 1890 Census, which had way more denominational choices than the 1950 version:

Image Link

[RI]

The last time the US Census asked about religion:

What is your data source?

National Historical Geographic Information System, run by the University of Minnesota. All their data is free, though you have to register.