The fuel filter on a 1987 Chevy S10 Blazer is typically located
on the frame rail, near the fuel tank. However, the exact location can vary slightly depending on the engine and specific options. It's often a cylindrical canister, and you might find it easier to locate by following the fuel line from the tank towards the engine.
To be sure, consult your owner's manual or a repair manual specific to your 1987 S10 Blazer. A diagram showing the fuel system will pinpoint its location precisely.