Complex sentence: In the United States, Leon Day is the halfway mark to Christmas ("Leon " is"Noel" spelled backwards) and is celebrated on June 25th, i.e. the turning point when Christmas begins to come closer on the calendar.
Split into simpler sentences: In the United States, Leon Day is the halfway mark to Christmas. It is celebrated on June 25th, i.e. the turning point when Christmas begins to come closer on the calendar.