Flag Observances for April
The US Flag is recommended to be flown on all days, but especially on federal and state holidays or observances. These are the federal observances and state holidays in April.
Good Friday: April 15. The following states officially designate Good Friday as a state holiday:
Connecticut, Texas, Delaware, Hawaii, Indiana, Tennessee, Florida, Kentucky, Louisiana, New Jersey, North Carolina, and North Dakota.
Admission Day: Maryland, April 28.
Easter Sunday: April 17.
Though these holidays are drawn directly from the Western Christian tradition (other Christian sects using the Julian or other calendars calculate different dates), federal and state courts have repeatedly weighed in that except for Easter in the US Flag Code, the legislative history of the state holidays is murky and goes back well over one hundred years. Thus, by tradition, Good Friday is considered Constitutional in the states which designate it a state holiday.
Due to the Julian Calendar, Orthodox churches celebrate Easter thirteen days later than Catholic or Protestant Churches. Orthodox Christianity also prohibits celebrating Good Friday on Passover (which occurs this year).
A movement started in the XX Century leading to current meetings between the Catholic, Orthodox, Syriac, Anglican, and Coptic churches to fix a permanent date for Easter (and thus Good Friday) has led to meetings in this century to achieve that. The most common date proposed is the Sunday after the second Saturday in April. So far, an agreement remains elusive between the sects, and it is unclear if Protestant churches would adopt any such agreement.
Easter Sunday is not a federal holiday though it is designated in the US Flag Code. Christmas Day is the only religious federal holiday in the United States.