Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
March 23 Maundy Thursday
March 24 Good Friday
March 26 Easter
March 27 Easter Monday
May 04 Feast of the Ascension
May 14 Pentecost
May 15 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions