Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 18 Maundy Thursday
April 19 Good Friday
April 21 Easter
April 22 Easter Monday
May 30 Feast of the Ascension
June 09 Pentecost
June 10 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions