Frederick Ludi and John Goller were the first settlers of the Upper Kittitas Valley. Their original plan was to go from the Cascade Mountains to the Puget Sound, but they ended up at Manastash Creek. They lived there for a year but decided to relocate due to their inability to adapt to the cold winters and heavy snow that came with the area. After they moved on from Manastash Creek, they eventually found what is now Ellensburg in 1867. He built a small cabin that would later be turned into Robber's Roost in 1870.

Fielden Mortimer (F.M) Thorp originally lived in Moxee where he made a living off of cattle. After the winters of the 1860s, the cattle had been severely damaged and it was a struggle to rebuild. It was in 1869 when Thorp moved to Taneum Creek with his family, where the town of Thorp would be discovered. With them was Charles Splawn as he married Thorp's daughter, Dulcina Thorp, in 1863. From there, the community of Thorp was on its way to becoming a bigger area with its agricultural potential and incoming settlers.

Thorp Mill, a four-story gristmill, was built by Oren Hutchinson and opened its doors in April 1883. This mill was able to provide farmers in the valley for convenience of wheat and as a community meeting location for fun activities. Thorp Mill was located to utilize the Yakima River water from the canal. A water wheel powered the mill and a nearby sawmill. There was also an ice pond and log pond close to the mill. The ice pond was unutilized as a recreational skating area and harvests for ice to chill train cars that would deliver produce to the market.

Kittitas Valley farmers made regular trips to the Thorp Mill with wagons full of wheat, later turned into flour, bran, or feed for livestock. In 1895 was the year that the Northern Pacific Railroad made transportation and delivery more efficiently with steel roller burrs. Local farmers were able to deliver to not only Thorp but throughout the Puget Sound region.

In 1906, the water wheel was able to power a steam generator, producing enough electrical power to get two morning laundry trips and giving homes light for a couple of hours. Thorp was one of the first towns in Washington to get electricity. The Thorp Mill had been in operation up until 1946, and was listed in the National Register of Historic Places on November 23, 1977.

In 1987, the mill board hosted fundraisers to maintain and restore the building, gaining support from organizations like the Washington State Legislature, Washington State Office of Historic Preservation, and the Lorene M. Petrie Trust in the following years. 1993 saw the opening of the Thorp Mill Museum to the public. More restoration efforts came in 2016 when Valerie Sivinski awarded the Mill $6,000 to repair the basement. Another donation came from the Suncadia Community Enhancement Fund in 2018 to build a storage unit on the ice pond property.

Seeing a need for irrigation in Thorp, Albert K. Owens created a survey of the land in 1889 that was inspired by a general irrigation plan written up a few years before. This was followed by a second survey a few years later. Both of these surveys had the underlying idea that Thorp could undertake the construction of the irrigation system through a private corporation. This would later be supported through the Act of Congress of 1902, commonly known as the "Reclamation Act", which had the intent of taking on the construction task.

The Yakima river was not sufficient to provide a water supply to the area of Thorp, and the United States government had taken notice of this. They had suggested creating storage water at Lake Kachess and Keechelus, but as the Interior department realized they didn't have enough funds to support these projects, they focused on the storage of water instead of distribution of said water. Congress supported these efforts in February 21, 1911 with the "Warren Act", authorizing the Secretary of the Interior ro deliver storage water to irrigation districts, private corporations, and those who paid a fee.

The Secretary of the Interior sent a letter ensuring that the proposed formation of the Kittitas Reclamation District would be supported on June 19, 1911. He made it a point that the district would be able to build all the systems they set out to create and meet the demands of the storage water. On September 14, 1911, the Kittitas Reclamation District had been voted into being organized almost unanimously. The board of directors had received $5,000,000 for the completion of the irrigation systems, property rights, and other costs.

In the early years of Thorp, it was a farming town with about 200 residents, nine miles northwest of Ellensburg. The main railroad of the Northern Pacific passed through Thorp, creating easy transportation and making the town an important point for shipping in the Upper Kittitas valley. Being a small manufacturing center, Thorp also had the advantage of having a flour mill, two sawmills, and a creamery. Smith J. Kendall and Joseph D. Mack owned and operated the flour mill, being able to export and ship items throughout the Upper Kittitas valley. Louis Ellison & J.L. Mills owned the sawmills, and the Wipple Brothers owned the creamery. Other businesses included general merchandise, two hotels, a blacksmith shop, feed stables, a stationery, a physician, surveyors, painters, and a saloon. The two churches in the Thorp were Principal W.C Thomas, a Methodist church, and Mary Peaslee, a Christian denomination. The Post Office was established in 1890.

Easton was platted on July 9, 1895 by John M. Newman alongside his wife Sarah Isabel Newman. On May 1, 1900 Milford A. and Amanda Thorp dedicated the town's name in honor of Fielden Mortimer (F.M.) Thorp. Milford A. Thorp, a pioneer of Yakima County, permanently settled in the Kittitas valley in 1879.

In the spring of 1887, the Northern Pacific Railroad finished the Cascade Branch through the Kittitas Valley, establishing an agricultural connection between the Columbia Basin, Tacoma and Pacific areas. After this was made, a new depot was created in the Northern Pacific named Thorp, after the pioneer Fielden Mortimer Thorp. Thorp was able to grow into the area that it is today. The ice harvests had also begun to see an increase of business during this time.

This economic boost ended in the 1950s when the Northern Pacific Railroad depot closed, later declining more in the 1960s with the interstate highway opening. Another factor that led to the decline of Thorp was the series of fires that destroyed the industrial areas. To this day, Thorp gets its identity from maintaining an independent school district, the mill, a post office, and the county's first fire department.

The earliest record of School District 9 of Yakima County was on April 5, 1874 in a letter from W. H. Crockett, approving the district becoming a recognized organization. Soon after the formation of this district, a call to action was soon made to divide the district into a southern portion on its own. This southern portion would later become the foundations of Thorp School District.

January 11, 1875 saw a petition to divide District 9 sent to the Yakima County superintendent of schools, who would approve this motion and create what was called the "Thorpe District" at the time. F.M. Thorp was one of twelve people who voted to approve this petition. This division was the cause of much confusion up until January 1880 when George W. Parrish approved of District 10's formation near Taneum Creek. The southern portion would become the entirety of District 9.

On November 7, 1887 District 9 purchased a one-acre property from William Andrew Forgey, near where the modern day Thorp Cemetery is, and built a schoolhouse here. Between 1887 and 1891, This new schoolhouse would be called the "Mills School". This schoolhouse construction was unlike most buildings in the district as it wasn't a log school. It was a painted shiplap sided house with fourteen-foot high ceilings, providing the community with a school that could inspire pride.

The 1890s saw the population of school children in the County growing at a high rate. By 1895 the enrollment for schools was at 2,408 students in the county. In response to the rise in students, districts became larger and new ones were being established. By the end of the 1890s, Kittitas County had 51 school districts. After Thopr was officially established as a town, the Thorp School District voted to move Mill's Schoolhouse half a mile closer to the town. To ease the tension that came from this new idea, District 46 was formed, cutting Thorp off from a schoolhouse. The next three years would have District 9 having no proper school building.

In the Spring of 1900, the first Thorp Schoolhouse was finished, located a little west from the town. 1904 saw the reuniting of Districts 46 and 9, becoming the first consolidated school district in Kittitas County. District 27 became a "Union School" equipped with a quality high school. This new school had the capacity of 200 students. In 1917, Thorp School District consolidated with the Splawn District, forming District 45. The school district would grow again in 1929, becoming District 102.

By 1932, enrollment rates had surpassed the capacity of the Thorp Schoolhouse at that time, and a plan to build a new brickhouse school to be completed in 1935. This would be the first brick building in Thorp. Victor Karlson, superintendent of the Thorp School District during the 1930s, claimed that the new school cost $41,000.

In the fall of 1936, Thorp Grade School had opened its first classes, providing education for up to the eighth grade. The gymnasium was the location used for sports and event space for the Thorp School District students. A nearly example for this was on November 11,1936 as the school held its annual Armistice Day program. In the 1950s, the high school building was remodeled from a two-story wooden building to a one-story modern high school building. More remodels occurred from the 1980s to 1990s, one of which was expanding the gymnasium. While most aspects from the campus were changed, the grade school building was mostly untouched.

Today, the Thorp Grade School is still used as the elementary school for the Thorp School District #400, as well as a reunion building for alumni. The alumni of Thorp Grade School used their testimonies to keep the rural community of Thorp well preserved. The school had been the embodiment of the commonly held belief in Thorp that public education was a top priority. It was highly focused on public and athletic education, seeing as the grade school and gymnasium were two of the highest employers in Thorp.