1771, in the book True Christian Religion, by Emanuel Swedenborg.
The first church built as a New Church place of worship, in Birmingham, England, was opened on the 19th June 1791. This was only noticed afterwards as a coincidence and was not a conscious decision.
The day is celebrated with religious services, pageants, banquets, and picnics.
There is even a New Church calendar system which uses 19th June 1770, as day 1 of year one. This would make 19th June 2013 New Year's Day in year 243 on the New Church calendar.