Ignoring spurious belts like secondary, interim, and franchise there are 18 current southpaw world titlists:

Billy Joe Saunders ENG WBO Super-Middle
Demetrius Andrade USA WBO Middle
Patrick Teixeira BRA WBO Super-Welter
Errol Spence Jnr USA IBF/WBC Welter
Terence Crawford USA WBO Welter
Manny Pacquiao PHI WBA Welter
Josh Taylor SCO WBA/IBF S-Light
Gervonta Davis USA WBA S-Feather
Joseph Diaz USA IBF S-Feather
Jamel Herring USA WBO S-Feather
Gary Russell Jnr USA WBC Feather
Luis Nery MEX WBC S-Bantam
Murodjon Akhmadaliev UZB WBA/IBF S-Bantam
Nordine Oubaali FRA WBC Bantam
Jerwin Ancajas PHI IBF Super-Fly
Junto Nakatani JAP WBO Fly
Pedro Taduran PHI IBF Straw
Wilfredo Mendez PR WBO Straw

There have been 265 southpaw world champions from 46 different countries with the leading countries being USA, 72, Mexico, 24, Philippines, 21, Japan, 20 and Thailand, 18.

Read A Brief History of Southpaws here