Metal detectors were installed for the first time this month at Trinity Church and St Paul's Chapel. The Rev Phillip Jackson said they will be there "until this world becomes a safer place".
Trinity and St Paul's are both part of the same Episcopal parish where George Washington and Alexander Hamilton worshipped after the American Revolution.
Church officials said the decision to install the metal detectors was not a response to any specific threat, but the Rev Jackson said a terrorist attack on a nearby bike path in the autumn was "kind of a wake-up call".
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