Hilo (/ˈhiːloʊ/; Hawaiian pronunciation: [ˈhilo]) is the largest town and census-designated place (CDP) in Hawaii County, Hawaii, United States, which encompasses the Island of Hawaiʻi. The population was 43,263 according to the 2010 census.^[1]

Hilo is the county seat of the County of Hawaiʻi and is in the District of South Hilo.^[2] The town overlooks Hilo Bay, at the base of two shield volcanoes, Mauna Loa, an active volcano, and Mauna Kea, a dormant volcano. Mauna Kea is the site of some of the world's most important ground-based astronomical observatories. Much of the city is at risk from lava flows from Mauna Loa. The majority of human settlement in Hilo stretches from Hilo Bay to Waiākea-Uka, on the flanks of the volcano.

Hilo is home to the University of Hawaiʻi at Hilo, ʻImiloa Astronomy Center of Hawaiʻi, as well as the Merrie Monarch Festival, a week-long celebration of ancient and modern hula that takes place annually after Easter. Hilo is also home to the Mauna Loa Macadamia Nut Corporation, one of the world's leading producers of macadamia nuts. The town is served by Hilo International Airport.^[3]

Around 1100 AD, the first Hilo inhabitants arrived, bringing with them Polynesian knowledge and traditions. Although archaeological evidence is scant, oral history has many references to people living in Hilo, along the Wailuku and Wailoa rivers during the time of ancient Hawaii.^[4] Oral history gives the meaning of Hilo as "to twist".^[5]

Originally, the name "Hilo" applied to a district encompassing much of the east coast of the island of Hawaiʻi, now divided into the District of South Hilo and the District of North Hilo. When William Ellis visited in 1823, the main settlement there was Waiākea on the south shore of Hilo Bay.^[6] Missionaries came to the district in the early-to-middle 19th century, founding Haili Church.

Hilo expanded as sugar plantations in the surrounding area created jobs and drew in many workers from Asia, making the town a trading center.

A breakwater across Hilo Bay was begun in the first decade of the 20th century and completed in 1929. On April 1, 1946, a 7.8-magnitude earthquake near the Aleutian Islands created a 46-foot-high (14 m) tsunami that hit Hilo 4.9 hours later, killing 160 people. In response, an early warning system, the Pacific Tsunami Warning Center, was established in 1949 to track these killer waves and provide warning. This tsunami also caused the end of the Hawaii Consolidated Railway, and instead the Hawaii Belt Road was built north of Hilo using some of the old railbed.^[7]

On May 22, 1960, another tsunami, caused by a 9.5-magnitude earthquake off the coast of Chile that day, claimed 61 lives,^[8] allegedly due to the failure of people to heed warning sirens. Low-lying bayfront areas of the city on Waiākea peninsula and along Hilo Bay, previously populated, were rededicated as parks and memorials.

Hilo expanded inland beginning in the 1960s. The downtown found a new role in the 1980s as the city's cultural center with several galleries and museums opening; the Palace Theater reopened in 1998 as an arthouse cinema.

Closure of the sugar plantations (including those in Hāmākua) during the 1990s hurt the local economy, coinciding with a general statewide slump. Hilo in recent years has seen commercial and population growth.

Hilo is on the eastern side of the island.^[9] It is classified by the U.S. Census Bureau as a census-designated place (CDP), and has a total area of 58.3 square miles (151.0 km2), 53.4 square miles (138.3 km2) of which is land and 4.9 square miles (12.7 km2) of which (8.4%) is water.^[10]

Hilo has a tropical rainforest climate (Köppen Af), with substantial rainfall throughout the year. Its location on the windward coast (relative to the trade winds), makes it the fourth-wettest city in the United States, behind the southeast Alaskan cities of Whittier, Ketchikan and Yakutat, and one of the wettest in the world. An average of around 126.72 inches (3,220 mm) of rain fell at Hilo International Airport annually between 1981 and 2010, with 272 days of the year receiving some rain.^[11] Rainfall in Hilo varies with altitude, with more at higher elevations. At some weather stations in upper Hilo the annual rainfall is above 200 inches (5,100 mm).^[12]

Monthly mean temperatures range from 71.2 °F (21.8 °C) in February to 76.4 °F (24.7 °C) in August.^[11] The highest recorded temperature was 94 °F (34 °C) on May 20, 1996, and the lowest 53 °F (12 °C) on February 21, 1962.^[13] The wettest year was 1994 with 182.81 inches (4,643.4 mm), and the driest was 1983, with 68.09 inches (1,729.5 mm). The most rainfall in one month was 50.82 inches (1,290.8 mm) in December 1954. The most rainfall in 24 hours was 27.24 inches (691.9 mm) on November 2, 2000.^[14]

Hilo's location on the shore of the funnel-shaped Hilo Bay also makes it vulnerable to tsunamis.^[15]

As of the census of 2010, 43,263 people lived in 15,483 households in the census-designated place. The population density was 796.7 people per square mile (307.7/km²). The 16,905 housing units reflected an average density of 311.3 per square mile (120.2/km²).

The racial makeup was 17.61% White, 0.52% African American, 0.31% American Indian & Alaska Native, 34.29% Asian, 14.17% Native Hawaiian & Pacific Islander, 0.60% from other races, and 32.51% from two or more races. Hispanic or Latino of any race were 10.40% of the population.^[1]

24.3% of the households had children under the age of 18 living with them. The average household size was 2.79.^[1]

The age distribution was 21.3% under age 18, 11.3% from 18 to 24, 11.5% from 25 to 34, 16.9% from 35 to 49, 20.9% from 50 to 64, and 18.0% 65 or older. The ratio of females to males was 100:95.5.^[1]

The median household income at the 2000 census was $39,139, while the median family income was $48,150. Males had a median income in 2000 of $36,049 compared to $27,626 for females. The per capita income was $18,220. About 11.1% of families and 17.1% of the population were below the poverty line, including 23.5% of those under age 18 and 6.7% of those age 65 or over.

Hilo is served by Hilo International Airport, where Hawaiian Airlines and United Airlines operate.

Hilo is served by the county Hele-On Bus.^[19]

Hilo is served by the Big Island's largest harbor, Hilo Harbor, on Hilo Bay.^[20]

Hilo is home to a number of educational institutions, including two post-secondary institutions, the University of Hawaiʻi at Hilo and Hawaiʻi Community College, and the Hilo and Waiakea primary and secondary school districts. Charter schools in the area serve primary and secondary students.

Although sometimes called a city, Hilo is not an incorporated city, and does not have a municipal government. The entire island, which is between the slightly larger state of Connecticut and smaller Rhode Island in size, is under the jurisdiction of the County of Hawaiʻi, of which Hilo is the county seat.

Hilo is home to county, state, and federal offices.

The oldest city in the Hawaiian archipelago, Hilo has a significant tourism sector.^[21] It is home to Hawaii's only tsunami museum, mostly dedicated to the 1946 Pacific tsunami, and is notable for the banyan trees planted by Babe Ruth, Amelia Earhart and other celebrities. It is home to the Pana'ewa Rainforest Zoo, shopping centers, cafés and other eateries, movie theaters, hotels, restaurants, and a developed downtown area with a Farmers Market.^[22]

The Mauna Loa Macadamia Nut Corporation makes its home there as well, south of the main town off Hawaii Route 11, north of Keaʻau.

Hilo is known for the Mokupāpapa Discovery Center ^[33] in the Koehnen Building downtown. The museum features interactive and educational exhibits and is dedicated to creating public awareness of the Papahānaumokuākea Marine National Monument and marine conservation issues.

Hilo is home to astronomical observatories on Mauna Kea as well as the Imiloa Planetarium and Museum. Astronomy has an economic impact of $100 million annually on the island.^[23] Astronomy on Mauna Kea was developed at the invitation of the Hawaii Chamber of Commerce following the collapse of the sugar cane industry.^[24]

Hilo is served by KWXX (94.7FM Hilo/101.5FM Kona), KWXX ^[34] , B93/B97 (93.1FM Kona/97.1FM Hilo), Hawaii's Classic Hits, B93/B97 ^[35] , and KPUA (970AM Hilo), Hilo's Sports Talk Radio KPUA 670AM ^[36] radio stations.

The Hawaii Tribune-Herald, of Oahu Publications Inc., a subsidiary of Black Press,^[26] is Hilo's primary newspaper distribution company along with other newspapers like the Honolulu Star-Advertiser.

Asteroid (342431) Hilo is named after Hilo.^[27]

Hilo also referred to the District of Hilo when the Big Island was divided into six districts by the traditional moku land division. Hilo is now divided in two: North and South Hilo Districts.^[28]

The District of North Hilo, along Hawaii State Highway 19 from north to south, encompasses the following unincorporated towns and localities:

and others. Inland, along State Highway 200, are Mauna Kea mountain road and Puu Huluhulu and others.

In the District of South Hilo, along State Highway 19, are the following unincorporated towns and localities:

Along State Highway 11, are:

and others. Along State Highway 200 and its extension, are:

and others.