Congregation Ezras Israel of Rockville, MD / Washington, D.C, 803 Montrose Road, Rockville, MD, US. 221 plaques total.
Ezras Israel was founded in Washington, DC in 1907. It moved to Northwest DC in the 1950s, and then to Silver Spring, Maryland. The long-time retired rabbi moved to Rockville, Maryland in 1978, where he founded Congregation Ezras Israel of Rockville, which currently houses the memorial plaques.
Most of the plaques are glass - they were fitted into a cabinet that would illuminate from behind the ones for which there was a yahrzeit that particular week. The cabinet was used at the 8th & I Streets location. There is also a more standard yahrzeit board from one of the later locations. The glass plaques are stored in a box; the yahrzeit board is currently in use at the Rockville congregation.
Article about yahrzeit cabinet
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The yahrzeit cabinet