Just to expand on what TR4a said, if it's a -300 with no winglets there's a 50% chance of one jumpseat; if it's a -300 with winglets 10% chance of one jumpseat; if it's a -500 there's two jumpseats; if it's a -700 10% chance of one jumpseat; if it's an -800 there's two jumpseats.
Every airplane SWA has received new from Boeing comes with two jumpseats (unlike another airline around here that shall remain nameless).