Despite seeing his fortune rise an additional $1.5 billion over the past year, Mayor Michael Bloomberg has dropped a few notches on Forbes 400 list of the wealthiest Americans.

Conservative businessman David Koch once again beat out Mayor Bloomberg to be the richest New Yorker.

Despite a net worth of $19.5 billion, Bloomberg actually fell two spots on this year's list to number 12.

Bill Gates is number one for the 18th year in a row.

The Microsoft chairman is worth $59 billion.

Facebook founder Mark Zuckerberg added $10.6 billion to his coffers this year, pushing his net worth to $17.5 billion.