Grant County is a county located in the U.S. state of Washington. As of the 2020 census, the population was 99,123. The county seat is Ephrata, and the largest city is Moses Lake. The county was formed out of Douglas County in February 1909 and is named for U.S. President Ulysses S. Grant.

Grant County comprises the Moses Lake, WA Micropolitan Statistical Area, which is also part of the Moses Lake-Othello, WA Combined Statistical Area.

Native American cultures in the area included the Interior Salish, Wenatchi, and Okanagan. The first white settlers began to arrive in the mid-to-late-19th century, primarily with the goal of raising livestock. One government official described the area in 1879 as, "…a desolation where even the most hopeful can find nothing in its future prospects to cheer."

When railroads arrived they also brought new settlers, and the economy began a shift from ranching to dryland farming. This transition required the people to have ready access to water, and irrigation became a necessity. The first large-scale irrigation attempts began in 1898, but it would be years before real success.

With the influx of dryland farming, the county soon boasted access to three major railway systems; the Great Northern Railway, Northern Pacific Railroad and the Chicago, Milwaukee & St. Paul Railroad. In addition, the Columbia River in this area was navigable. This allowed crops to be transported out of the area easily. Towns like Wilson Creek, Quincy and Ephrata began to thrive.

The Washington State Legislature officially created Grant County on February 24, 1909, naming it in the memory of Ulysses S. Grant, the 18th president of the United States, and a major contributor to the Union victory in the American Civil War. The county seat was located in Ephrata. The area's population at the time stood at around 8700 people.

The Columbia Basin Project, which ultimately produced the Grand Coulee Dam with its associated irrigation and hydroelectric generating grid, was an outgrowth of the 1902 creation of the United States Bureau of Reclamation. When that agency began studying feasibility of projects in the Northwestern United States, competing groups from Spokane, Wenatchee, Ephrata and elsewhere advanced competing possibilities. One idea was to dam the Columbia River at Grand Coulee. This concept was approved in 1933, and construction continued in the following decades. The project would fundamentally change the region forever.

According to the United States Census Bureau, the county has a total area of 2,791 square miles (7,230 km), of which 2,680 square miles (6,900 km) is land and 112 square miles (290 km) (4.0%) is water. It is the fourth-largest county in Washington by area.

The environmental climate of Grant County is characterized by hot summers and cold winters. Rainshadow caused by the Cascade mountains separates eastern Washington, including Grant County, from western Washington's more temperate and oceanic climate.

A sign alongside Interstate Highway I-90 where it enters Grant County welcomes travelers to Grant County and says the county is "The nation's leading potato producing county".

• Columbia River
• Grand Coulee
• Moses Lake
• Potholes Reservoir
• Soap Lake
• Ulysses S. Peak, unofficial name of county high point

• I-90
• I-90 BL
• U.S. Route 2
• State Route 17
• State Route 28

• Columbia National Wildlife Refuge (part)
• Hanford Reach National Monument (part)
• Lake Roosevelt National Recreation Area (part)
• Saddle Mountain National Wildlife Refuge (part)

Historical population

Census	Pop.	Note	%±
1910	8,698		—
1920	7,771		−10.7%
1930	5,666		−27.1%
1940	14,668		158.9%
1950	24,346		66.0%
1960	46,477		90.9%
1970	41,881		−9.9%
1980	48,522		15.9%
1990	54,758		12.9%
2000	74,698		36.4%
2010	89,120		19.3%
2020	99,123		11.2%
2023 (est.)	102,678		3.6%
U.S. Decennial Census 1790–1960 1900–1990 1990–2000 2010–2020

As of the 2020 census, there were 99,123 people and 32,803 households in the county. The population density was 37.0 people per square mile (14.3 people/km). The racial makeup of the county was 90.8% White, 1.3% Asian, 2.7% American Indian, 2.2% African American, 0.3% Pacific Islander, and 2.7% from two or more races. Those of Hispanic or Latino origin made up 43.6% of the population.

28.3% of the population of the county was under 18, and 7.1% were under 5. People over 65 represented 14.7% of the population. The gender ratio was equal, with 48.9% of the population being female and 51.1% being male.

The median income for a household in the county was $63,566, and the per capita income was $27,466. 11.7% of the population was below the poverty line.

As of the 2010 census, there were 89,120 people, 30,041 households, and 21,800 families living in the county. The population density was 33.3 inhabitants per square mile (12.9/km). There were 35,083 housing units at an average density of 13.1 per square mile (5.1/km). The racial makeup of the county was 72.8% white, 1.2% American Indian, 1.1% black or African American, 0.9% Asian, 0.1% Pacific islander, 20.4% from other races, and 3.5% from two or more races. Those of Hispanic or Latino origin made up 38.3% of the population. In terms of ancestry, 15.5% were German, 8.9% were English, 7.1% were Irish, and 3.9% were American.

Of the 30,041 households, 40.6% had children under the age of 18 living with them, 54.7% were married couples living together, 11.5% had a female householder with no husband present, 27.4% were non-families, and 22.0% of all households were made up of individuals. The average household size was 2.93 and the average family size was 3.40. The median age was 32.1 years.

The median income for a household in the county was $42,572 and the median income for a family was $50,065. Males had a median income of $39,530 versus $27,417 for females. The per capita income for the county was $19,718. About 15.7% of families and 20.4% of the population were below the poverty line, including 28.4% of those under age 18 and 7.2% of those age 65 or over.

School districts in the county include:

Grant County is a reliably Republican county in presidential elections; it has not voted for the Democratic candidate since Lyndon B. Johnson's landslide victory in 1964. It has cast at least 60% of its vote for the Republican presidential candidate in all six elections since 2000.

United States presidential election results for Grant County, Washington

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2020	24,764	65.72%	11,819	31.37%	1,097	2.91%
2016	18,518	63.29%	7,810	26.69%	2,930	10.01%
2012	17,852	64.15%	8,950	32.16%	1,027	3.69%
2008	17,153	62.07%	9,601	34.74%	880	3.18%
2004	17,799	68.47%	7,779	29.92%	417	1.60%
2000	15,830	66.52%	7,073	29.72%	895	3.76%
1996	10,895	49.83%	8,065	36.88%	2,906	13.29%
1992	9,503	43.35%	7,278	33.20%	5,140	23.45%
1988	10,859	57.76%	7,564	40.24%	376	2.00%
1984	12,888	65.81%	6,298	32.16%	398	2.03%
1980	11,152	61.29%	5,673	31.18%	1,371	7.53%
1976	9,192	51.87%	7,777	43.89%	752	4.24%
1972	9,370	59.25%	5,487	34.70%	957	6.05%
1968	7,007	48.77%	5,773	40.18%	1,587	11.05%
1964	6,065	42.04%	8,352	57.89%	10	0.07%
1960	7,568	50.44%	7,400	49.32%	37	0.25%
1956	6,603	48.73%	6,938	51.21%	8	0.06%
1952	4,512	50.61%	4,381	49.14%	22	0.25%
1948	2,081	33.15%	4,067	64.79%	129	2.06%
1944	1,530	39.21%	2,354	60.33%	18	0.46%
1940	1,487	26.55%	4,097	73.15%	17	0.30%
1936	694	13.03%	4,560	85.59%	74	1.39%
1932	840	34.85%	1,376	57.10%	194	8.05%
1928	1,407	68.07%	641	31.01%	19	0.92%
1924	813	40.87%	332	16.69%	844	42.43%
1920	1,378	58.24%	684	28.91%	304	12.85%
1916	1,205	39.77%	1,563	51.58%	262	8.65%
1912	458	17.41%	771	29.32%	1,401	53.27%

Grant is the #1 crop-producing County in the State, producing a large part of the Washington hay harvest.

• Grant County Public Utility District
• National Register of Historic Places listings in Grant County, Washington

• Grant County – official website
• Photos of Grant County Archived May 18, 2006, at the Wayback Machine
• Grant Transit Authority

47°13′N 119°28′W / 47.21°N 119.47°W / 47.21; -119.47