Why is it called the 21st century?

1ST FNCL Bank USA 7 22nd State Bank Company 2 Applied Bank 8 BONVENU Bank National Association 4 Carver State Bank 9 Cattlemens Bank 6 Cecil Bank 7 CentreBank 3 Citizens Bank, Edinburg 2 CTBC Bank CORP USA 22 Four County Bank 4 KLEBERG Bank National Association 4 McBank 11 Nebraska Bank of Commerce 3 Northeast Security Bank 2 OptimumBank 19 Patterson State Bank 4 Potomac Bank 2 SOUTHWEST MO Bank 8 WASHINGTON Trust Bank 9