Where is block heater located in 2001 Saturn 3-DOOR SC?

IF there is a block heater (Only some models had block heaters) you will see the electrical plug wound up somewhere under the hood. Follow that wire back to where the block heater goes into the block.

If your Saturn doesn't have a block heater, and you want one, there are several options.

You can purchase a block heater that replaces the engine freeze plug. That requires installation by a qualified mechanic since the old freeze plug must be removed to use that style block heater.

You can purchase an engine heater that fits inline with the coolant system. That just requires cutting a hose and splicing in the engine heater.

You can purchase an engine heater that sticks magnetically to the engine while in use. Be careful with that model since you should remove it if it's hanging down from the bottom; it could become a hazard when you're driving.