Q: Parish Patronal day (usually occurring on a weekday)…Feast or Solemnity?…I would presume that the answer would indicate whether the Creed is used, or omitted…
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A: It depends.
The proper solemnity is the date associated with the title of the church at its dedication. Some parishes have regrouped since dedication and are known by other names. But the title of the church never changes.
If the parish patron is the title, then the date is observed as a solemnity. If not, it may be a feast.