There were to be jugglers, stilt walkers and puppets of giant butterflies, all marching down Maple Avenue in South Plainfield, N.J., in the town’s 62nd annual Labor Day parade.

Instead, as it started to rain on Monday, the festivities were abruptly canceled, not because of the weather, but because of something that now seems as common at this summer’s public gatherings as hot dogs and fried dough: fear.

Police had found explosive devices overnight near the home of a man who lived close to the staging area of the parade route, said Matthew P. Anesh, the mayor of South Plainfield, a town about 35 miles southwest of New York City, at a news conference on Monday afternoon.

The devices did not appear to be bombs, but were closer to homemade fireworks, according to a person familiar with the situation who requested anonymity because he was not permitted to discuss the ongoing investigation.