Nothing has dampened Bill Iffrig’s passion for running, not even surviving an event more vividly traumatic than many will experience in a lifetime—the 2013 Boston Marathon bombings.

Camera footage caught the moment of explosion, recording a sea of shocked runners, including one 78-year-old man thrown down by the blast a few minutes from the finish line.

That runner was Iffrig, and he will be in town later this month to run in the Smelt Derby 10K, hosted by the Rotary Club of La Conner.

Iffrig landed in the street on his back that day in Boston nearly four years ago. When he looked up, he...