How many people get killed by a tornado in America per year?

It varies from year to year. Looking at data for the past 30 years the average annual death toll for tornadoes in the U.S. is 74. The highest death toll in this period was 553 set in 2011, the second deadliest tornado year in U.S. history, while the lowest was 15, set in 1987.

Note that the 2011 season was highly unusual, as the next highest annual death toll was 132, set in 1998, and that if 2011 is excluded from calculations the average annual death toll is reduced to 57.