The box is located at the Park and Ride lot near Sycamore Valley Road and Camino Ramon.
It had been worked on earlier on Sunday, but was not properly closed and locked.
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The lid was left open for about an hour Sunday afternoon.
Town of Danville spokesperson said there's no evidence anyone's ballot went missing or was mishandled.
But if you dropped your ballot off and have concerns - you can contact the Contra Costa County registrar.
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