Per Hallmark - here are the number of cards sent for the major holidays

This chart provides Hallmark's estimates for U.S. greeting card industry statistics for the top card-sending holidays:

Rank / Holiday Number of Cards Sent
1. Christmas --------- 2.1 billion (including boxed and individual cards)
2. Valentine's Day --- 191 million (not including classroom valentines)
3. Mother's Day ------ 158 million
4. Father's Day ------- 102 million
5. Easter -------------- 88 million
6. Halloween --------- 35 million
7. Thanksgiving ----- 25 million
8. St. Patrick's Day -- 11 million