No official calendar but I can try to break it down for you.
-Early January (1st week): pretty high crowds on the 1st, and crowds start to decrease as kids start going back to school
-Rest of January: low crowds
-Early Feb: low crowds
-President's Weekend/Week: Weekend more crowded than week, but not an overwhelmingly popular holiday week.
-Late February: low crowds
-Early/Mid-March: medium sized crowds
-Spring Break (late March-mid April): One of the most crowded times of the year. Packed!
-Late April-(all of) May: medium-low crowds
-Early June: medium crowds, Grad Nights change up the park hours a bit
-Late June: CRAZY! Especially this past year, Late June was incredibly crowded
-Early July: High crowds, but not as high as late June
-July 4th: not as high crowds as you would expect
-Rest of July-Early/Mid August: High crowds, similar to Early July
-Late August: Very crowded right before schools start
-September: low crowds
-October: weekends very crowded, some parts of the month (Gay Days, Halloween, "Fall Break") can be pretty crowded, but weekdays have low crowds
-November: Low crowds, except Veteran's Day and Thanksgiving. Veteran's Day more crowded than Thanksgiving. Thanksgiving crowds similar to a summer weekday
-Early December: low crowds
-Late December: As Christmas gets nearer and nearer, the crowds increase daily.
-Last 7 days of the year: MOST crowded time of the year
That's a very basic rough outline of the crowd patterns at DLR.