It is impossible to determine an exact number. Record outside the U.S. are too incomplete to give any sort of answer. In the US there have been 1302 tornadoes recorded in December in the years 1950-2013. The actual number is likely higher since many of the less significant tornadoes before the 1980s and 1990s were missed.
Preliminary figures indicate that there were 1704 tornadoes in the U.S. in 2011, though the final count for December has yet to be released. worlwide the number is unknown.
There were 94 tornadoes in Alabama in 2008.
There were 105 tornadoes in Iowa in 2008.
There were 20 tornadoes in Ohio in 2014.
15 tornadoes occurred in Michigan in 2011.
There were 1,103 tornadoes in the U.S. in 2006.
There were 16 confirmed tornadoes in Arkansas in 2007.
There were 1,817 tornadoes recorded in the U.S. in 2004.
The U.S. had 1075 confirmed tornadoes in 2000.
There were 1374 tornadoes confirmed in the United States in 2003.
65 tornadoes occurred in North Carolina in 2011.
1,282 tornadoes occurred in the US. in 2010, with an unknown number worldwide.