Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 20 Maundy Thursday
April 21 Good Friday
April 23 Easter
April 24 Easter Monday
June 01 Feast of the Ascension
June 11 Pentecost
June 12 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions