Question: The Minimalists are authors who moved from their hometown to a cabin in the county seat of what Montana county?

Context paragraphs:
Seneca County, New York: Seneca County is a county located in the U.S. state of New York.  As of the 2010 census, the population was 35,251.  The primary county seat is Waterloo, moved there from the original county seat of Ovid in 1819.  It became a two-shire county in 1822, which currently remains in effect, using both locations as county seats although the majority of Seneca County administrative offices are located in Waterloo.  Therefore, most political sources only list Waterloo as the county seat.  The county's name is from the Iroquois (Seneca) that occupied part of the region.

Former Audubon County Courthouse: The Former Audubon County Courthouse, also known as the Audubon County Historical Society Museum, is a historic building located in Exira, Iowa, United States.  Court proceedings were first held in a schoolhouse in Hamlin’s Grove after Audubon County was established in 1851.  The county seat was relocated to Exira ten years later, and a disagreement erupted over where the county seat should be located.  The county board of supervisors made an appropriation for a new courthouse in 1871, but its construction was delayed due to the disagreement.  Exira eventually won and officials constructed the courthouse for about $2,200.  The Exira Hall Company was established to build the two-story, frame structure.  County offices were located on the first floor and the courtroom was located on the second floor.  The county seat was moved to Audubon in 1879.

Choteau, Montana: Choteau is a city in and the county seat of Teton County, Montana, United States.  It lies along U.S. Routes 89 and 287 (the latter terminating at the former in this city) about 20 mi east of the Rocky Mountains, near Flathead National Forest, the Rocky Mountain Division of Lewis and Clark National Forest, and Glacier National Park.  The population was 1,684 at the 2010 census.  The Montana town is named for French fur-trapper and explorer Pierre Chouteau, Jr., who is also the namesake of Chouteau County, Montana (county seat: Fort Benton).

Philipsburg, Montana: Philipsburg is a town in and the county seat of Granite County, Montana, United States.  The population was 820 at the 2010 census.  The town was named after the famous mining engineer Philip Deidesheimer, who designed and supervised the construction of the ore smelter around which the town originally formed.

Ohio County, West Virginia: Ohio County is a county located in the Northern Panhandle of the U.S. state of West Virginia.  As of the 2010 census, the population was 44,443.  Its county seat is Wheeling.  The county was formed from the District of West Augusta, Virginia in 1776.  It was named for the Ohio River, which forms its western boundary.  West Liberty (formerly Black's Cabin) was the county seat from 1777 to 1797.

Greencastle, Indiana: Greencastle is a city in Greencastle Township, Putnam County, Indiana, United States, and the county seat of Putnam County.  It was founded in 1821 by Ephraim Dukes on a land grant.  He named the settlement for his hometown of Greencastle, Pennsylvania.  Greencastle was a village or town operating under authority of the Putnam County commissioners until March 9, 1849, when it became a town by special act of the local legislature.  Greencastle, Indiana, officially became a city after an election held on July 8, 1861.  The first mayor of Greencastle was E. R. Kercheval, a member (during his lifetime) of the Freemason Temple Lodge #47.  The city became the county seat of Putnam County.  The population was 10,326 at the 2010 census.  It is located near Interstate 70 approximately halfway between Terre Haute and Indianapolis in the west-central portion of the state.  Greencastle is well known as being the location of DePauw University.

Confederate Gulch and Diamond City: Confederate Gulch is a steeply incised valley on the west facing slopes of the Big Belt Mountains in the U.S. state of Montana.  Its small stream drains westward into Canyon Ferry Lake, on the upper Missouri River Valley near present-day Townsend, Montana.  In 1864 Confederate soldiers on parole from the American Civil War made a minor gold discovery in the gulch, but in 1865 the discovery of the sensationally rich Montana Bar—one of the richest placer strikes per acre ever made—led to other rich gold strikes up and down the gulch, and touched off a frantic boom period of placer gold mining that extended through 1869.  From 1866 to 1869 the gulch equaled or outstripped all other Montana Territory mining camps in gold production, producing an estimated $19 to $30 million in gold—late 1860s money.  For a time, the gulch became the largest community in Montana—in 1866 Montana had a total population of 28,000, and of these, about 10,000 (35%) were working in Confederate Gulch.  The main community was Diamond City , and while gold production was at its height, Diamond City roared along both night and day.  During its heyday, Diamond City was the county seat of Montana's Meagher County, although today the area has become part of Broadwater County.  In their frantic efforts to get at more gold, the miners built ditches and flumes that extended for miles, and employed high pressure hydraulic mining methods which washed down whole hillsides and ate up the gulch floor.  The hydraulic mining process stripped the gulch and left huge spoil banks—hydraulic mining even consumed the site of Diamond City, which had to be moved to a new location.  Then the gold ran out, the boom was over and the population simply picked up and left.  In 1870 there were only 255 people left and a year later only about 60.  Today hardly a trace remains of Diamond City or the other gulch communities.  The gulch is quiet and empty, with only an occasional summer prospector, or a rare traveler using the unimproved road that still winds up the gulch from the Missouri Valley and crosses the top of the Big Belts on its way down to the Smith River Valley.  Diamond City, Confederate Gulch and the Montana Bar were spectacular examples of the flash-in-the pan Montana placer gold mining camps, but what a flash.

The Minimalists: The Minimalists are American authors, podcasters, filmmakers, and public speakers Joshua Fields Millburn and Ryan Nicodemus.  The duo began pursuing the minimalist lifestyle in 2010.  After experiencing significant improvements in their quality of life as a result of adopting and practicing the tenets of minimalism, the pair launched a website in December 2010 to share their experiences.  In late 2012 the pair moved from their hometown of Dayton, Ohio, to a cabin in Philipsburg, Montana, to focus on their writing.  After four months in Philipsburg, they moved to Missoula, Montana, where they still live and work today.

1724 Chester Courthouse: The old Chester Courthouse was built in 1724 in Chester, to serve as the courthouse for Chester County, Pennsylvania.  Chester County was one of the first three counties in the Province of Pennsylvania set up by William Penn.  About 1790 the county seat was moved to West Chester, Pennsylvania and the Chester Courthouse no longer served as the county courthouse.  A few years later, the area around Chester was separated from Chester County and formed into Delaware County, Pennsylvania and the Chester Courthouse became the courthouse for Delaware County.  In 1850 the county seat was again moved - this time to Media and Chester Courthouse served as City Hall for the city of Chester.

Cerro Gordo County Courthouse (Iowa): The Cerro Gordo County Courthouse is located in Mason City, Iowa, United States.  When Cerro Gordo County was created in 1855 and Mason City was selected to be the county seat.  Dissatisfaction in the western part of the county led the Iowa legislature to appoint three new commissioners who would move the county seat to Livonia.  A courthouse was built there.  A petition signed by over half of the citizens of the county requested that the county seat be moved back to Mason City.  Mason City also won the election in 1858 to decide the matter 155-48.  Two courthouses have stood in Mason City prior to the present Modernist structure that was occupied by the county in 1960.  It had been built as the Standard Oil Building, and was acquired by the county in 1959 for $159,400 and then remodeled for their use.

Supporting paragraphs: The Minimalists Philipsburg, Montana
Answer: Granite