There were 52 in the month of November alone.
56, but who is counting. Read on down the page:
"During the month of November 2003, 56 earthquakes were located in the Yellowstone region. The largest shock to occur during this report period was a magnitude 2.2 earthquake on November 20th at 14:26 UTC, located about 8.3 miles south southwest of Madison Junction, Wyoming.
"Earthquake activity in the Yellowstone region is at background levels."
http://volcanoes.usgs.gov/yvo/activity.html