This individual strongly resembled
this photo of Grassiella wheeleri when alive. I'm exceptionally curious because all the references I can find; including Borror, Triplehorn and Johnson's
An Introduction to the Study of Insects, 6th ed., say that all North American Nicoletiidae occur only in Texas and Florida.
I found this along with ~50 others in the early afternoon (between noon and 2). They were under a rotting board next to a nest of small ants of unknown type (unfortunately I don't know how to identify ants). They scurried like silverfish normally do and they didn't jump.
I'll post a picture (albeit a relatively poor one--I'm very new to photography) of an ant that I found with this specimen.
Note: the markings on the ruler below are 1/8 in., so the specimen is about 6 mm.