The Plymouth Society of Chicago selected a committee to investigate the irrigated Payette River Valley in the five-year-old state of Idaho, and another site in Colorado, to be purchased for the colony. The present city of New Plymouth was on the drawing boards in Chicago, designed as a town able to be self reliant through the use of irrigation, solidly built on an agricultural and railroad economy.
In February 1896, each colonist purchased 20 shares of stock at $30 per share, which entitled him to 20 acres of land and a town lot. He was to clear the land of sagebrush and plant fruit trees, preferably apples. The town was platted with a horseshoe shape with its open end facing to the north, toward the railroad and the river. This area was planned as an industrial zone, and the acre tracts around the horseshoe were the residential lots.
The homes were to built on the street side and the balance of the acre for garden and pasture for the family cow and the driving team. Two streets, separated by an 80-foot park, curve around the town in a horseshoe shape. This one-mile (1.6 km) long park and the streets that enclose it were called "The Boulevard." The park was planted with grass and shade trees. Plymouth Avenue, the main street and principal business thoroughfare, was surveyed (16 feet off the section line) down the center of the horseshoe from the railroad on the north through the Boulevard on the south.
The community was at first called the New Plymouth Farm Village and was governed by a colony board of directors until it incorporated as a village in 1908, dropping the last two words in the name. It was designated a city in 1948.
According to the United States Census Bureau, the city has a total area of 0.7 square miles (1.8 km²), all of it land.
There were 524 households out of which 38.0% had children under the age of 18 living with them, 56.1% were married couples living together, 10.7% had a female householder with no husband present, and 29.0% were non-families. 25.6% of all households were made up of individuals and 13.7% had someone living alone who was 65 years of age or older. The average household size was 2.67 and the average family size was 3.23.
In the city the population was spread out with 31.7% under the age of 18, 6.7% from 18 to 24, 27.9% from 25 to 44, 18.6% from 45 to 64, and 15.1% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 95.3 males. For every 100 females age 18 and over, there were 88.6 males.
The median income for a household in the city was $30,524, and the median income for a family was $33,224. Males had a median income of $28,529 versus $21,161 for females. The per capita income for the city was $12,624. About 12.3% of families and 17.2% of the population were below the poverty line, including 25.9% of those under age 18 and 8.9% of those age 65 or over.