Officially, Plymouth was settled in 1869 by 5 men who lived there the first summer in tents while their stock was enjoying the excellent grazing. In the fall, they laid out a one block townsite and each drew lots to pick their home site. That fall, 3 log cabins were built. The next year they built a reservoir and used the water to power a sawmill. Most of the lumber they produced went into building Bear River City and the first school in Plymouth (opened in 1871). Plymouth was part of the Portage Ward until 1884 when the church decided there were enough settlers in the area to warrant organizing their own ward (containing what is now Fielding, Riverside and Plymouth). It was about this same time that the first post office was established in Plymouth.

One story says the town got its name when some of the early pioneers were out taking a walk and came across a large rock. One of the women remarked that the rock resembled Old Plymouth Rock (in Massachusetts). They all thought about it for a bit and then decided that Plymouth was a good name for their community.