This movie is based on actual events that occurred between November 1966 and December 1967 in Point Pleasant, West Virginia.

The name of the expert on paranormal activity is Leek, the reverse of paranormal expert and author of the novel on which this movie was based, John A. Keel.

Lakeshore Entertainment cut two million dollars out of the budget just days before shooting began. Director Mark Pellington was furious, having vowed not to make the same concessions that plagued his previous movie, Arlington Road (1999).

The scene where Indrid Cold is seen for the first time in full wasn't done with CGI. Bill Laing was simply shot in blurred vision.

DIRECTOR CAMEO (Mark Pellington): The bartender, also the voice of Indrid Cold during the phone call.

The clock radio in John Klein's (Richard Gere's) motel room reads: 6:14. It's a Biblical reference to John Chapter 6 verse 14, which reads, "This is indeed the prophet who is to come into the world."

The news station, WOWK 13, shown during the Charleston scenes is the actual news station for the Charleston-Huntington area.

Contrary to popular belief, the Mothman wasn't originally described as a moth-like creature by the witnesses. At the time, the creature was described as half-bird and half-man. They also claimed that the creature had feathers and would make screeching noise.

The Mothman from 1966 and 1967 was originally named after the title of Batman (1966).

When John Klein (Richard Gere) has his first encounter with the Mothman, it results in a car accident when his car collides with a tree. The street is Bartlett Street in Squirrel Hill in Pittsburgh, Pennsylvania. The traffic signal they're approaching was put in for filming, and is no longer there.

Michael Gambon, John Hurt, David Suchet, and Charles Dance were considered for the role of Alexander Leek.

Richard Gere and Laura Linney appeared in Primal Fear (1996).

Director Mark Pellington, who did the voice of Indrid Cold, occasionally added his voice under the dialogue of characters who spoke on the phone with John Klein (Richard Gere) throughout the movie. Pellington said the intention was to create the illusion that Indrid Cold could be any one of those people, and that the entire situation, and all of the people might actually be in Klein's head.

At the end of the movie, it states that the cause of the bridge collapse was never determined. The real Silver Bridge is known to have collapsed due to a failure of I-bar 330 on the north of the Ohio subsidiary chain just below the top of the Ohio tower. The failure of a single I-bar brought the bridge down due to lack of redundancy in the design of the structure. Traffic loads far exceeded what the bridge was built to carry.

For the "bridge collapse" sequence, it took Camera Assistant for Fantasy II Gene Warren III and five other model makers, plus two production assistants three months to fabricate every piece of the bridge set from scratch. He estimates twenty thousand individual pieces of steel went into the construction, in order for the ultra-photo-realistic 1/6th scale model suspension bridge to support all of the model vehicles, and ultimately collapse like a full-scale steel bridge into the water. Of the hundreds of sets Gene has accomplished, this remains his favorite. The entire set was built spanning the water tank at Fantasy II.

The bridge collapse in this movie is stated to have killed thirty-six people. This is fewer than the real Silver Bridge collapse, which killed forty-six.

The Mothman's face appears six times in this movie. The first is when he flies into Mary's (Debra Messing's) face. The second is at the end of the scene where John (Richard Gere) is talking with the woman who saw Indrid through the window, the camera zooms out, and the scorch mark at the trees back left by the mothman has his face. The third is when the young couple describes the incident at the factory site, when the mothman moves off the car. The fourth is in the beginning of the zoom out from Mary's photograph after John had smashed the phone, the mothman's face and shape appears in Mary's pupil. The fifth is when he is seen in the mirror on the door that John slams. The sixth and final time is when the cable slams into the car windshield.

In this movie, the Silver Bridge collapsed at Christmas. In reality, it was on December 15.