Timeline of United States discoveries encompasses the breakthroughs of human thought and knowledge of new scientific findings, phenomena, places, things, and what was previously unknown to exist. From a historical standpoint, the timeline below of United States discoveries dates from the 18th century to the current 21st century, which have been achieved by discoverers who are either native-born or naturalized citizens of the United States.

With an emphasis of discoveries in the fields of astronomy, physics, chemistry, medicine, biology, geology, paleontology, and archaeology, United States citizens acclaimed in their professions have contributed much. For example, the "Bone Wars," beginning in 1877 and ending in 1892, was an intense period of rivalry between two American paleontologists, Edward Drinker Cope and Othniel Charles Marsh, who initiated several expeditions throughout North America in the pursuit of discovering, identifying, and finding new species of dinosaur fossils. In total, their large efforts resulted in when 142 species of dinosaurs being discovered. With the founding of the National Aeronautics and Space Administration (NASA) in 1958, a vision and continued commitment by the United States of finding extraterrestrial and astronomical discoveries has helped the world to better understand the Solar System and universe. As one example, in 2008, the Phoenix lander discovered the presence of frozen water on the planet Mars of which scientists such as Peter H. Smith of the University of Arizona Lunar and Planetary Laboratory (LPL) had suspected before the mission confirmed its existence.

Eighteenth century 1747 Charge conservation In physics, charge conservation is the principle that electric charge can neither be created nor destroyed. The quantity of electric charge, the amount of positive charge minus the amount of negative charge in the universe, is always conserved. As part of his groundbreaking work in electricity, Benjamin Franklin around the year 1747 discovered the principle of charge conservation when he came to the conclusion that the two states of electricity, positive and negative, the charge is never created or destroyed but instead transferable from one place to another.

1796 Johnston Atoll Johnston Atoll, a territory of the United States, part of the Pacific Islands Heritage Marine National Monument, and a part of the wider United States Minor Outlying Islands, is a 50-square-mile (130 km2) atoll in the North Pacific Ocean about west of the U.S. state of Hawaii. There are four islands located on the coral reef platform, two natural islands, Johnston Island and Sand Island, which have been expanded by coral dredging, as well as North Island (Akau) and East Island (Hikina), an additional two artificial islands formed by coral dredging. The sovereignty of Johnston Atoll was disputed and claimed by the Kingdom of Hawaii beginning in 1858 until Hawaii itself was eventually annexed by the United States as the Hawaii Territory in 1898. Johnston Atoll is now administered and managed by the United States Fish and Wildlife Service, an agency of the United States Department of Interior. In 1796, Johnston Atoll was discovered accidentally by U.S. Captain Joseph Pierpoint when his ship, the American brig Sally, ran aground.

1798 Tabuaeran Tabuaeran, also known as Fanning Island or Fanning Atoll (both Gilbertese and English names are recognized) is one of the Line Islands located in the central Pacific Ocean. With a population of approximately 2,500, much of the island's economy relies upon the cruise industry. Formerly under British rule, Tabuaeran now is a part of the Republic of Kiribati. Tabuaeran was discovered on June 11, 1798, by U.S. Captain Edmund Fanning, at 3 a.m., while on a voyage to China aboard his ship, Betsy.

1798 Teraina Teraina, also known as Washington Island, is an inhabited coral atoll located in the central Pacific Ocean that is north of the equator, northwest of Tabuaeran, northwest of Christmas Island, and southeast of the U.S. territory of Palmyra Atoll. Formerly under British rule, Teraina is now a part of the Republic of Kiribati. Obsolete names of Teraina are Prospect Island and New York Island. The island consists of nine Polynesian villages. Teraina was discovered by U.S. Captain Edmund Fanning, in the American ship Betsy, on June 12, 1798.

1798 Palmyra Atoll

Palmyra Atoll, a territory of the United States, part of the Pacific Islands Heritage Marine National Monument, and a part of the wider United States Minor Outlying Islands, is a atoll located in the North Pacific Ocean almost due south of the Hawaiian Islands, roughly halfway between the U.S. state of Hawaii and the U.S. territory of American Samoa. The atoll consists of an extensive reef, two shallow lagoons, and some 50 sand and reef-rock islets and bars covered with lush, tropical vegetation. The islets of the atoll are all connected, except Sand Island and the two Home Islets in the west and Barren Island in the east. The largest island is Cooper Island in the north, followed by Kaula Island in the south. Cooper Island is privately owned by The Nature Conservancy and managed as a nature reserve. The rest of the atoll is managed by the United States Fish and Wildlife Service and is directly administered by the Office of Insular Affairs, an agency of the United States Department of Interior. Palmyra Atoll's history is long and colorful. It was first sighted on June 14, 1798, by Captain Edmund Fanning and officially discovered in 1802 by Captain Sawle of the American ship Palmyra.

1798 Kingman Reef Kingman Reef, a territory of the United States, part of the Pacific Islands Heritage Marine National Monument, and a part of the wider United States Minor Outlying Islands, is a largely submerged, uninhabited triangular shaped reef, 9.5 nautical miles (18 kilometers) east-west and 5 nautical miles (9 kilometers) north-south, located in the North Pacific Ocean, roughly halfway between the Hawaiian Islands and the U.S. territory of American Samoa. It is the northernmost of the Northern Line Islands and lies 36 nautical miles (67 kilometers) northwest of the next closest island, the U.S. territory of Palmyra Atoll, and 930 nautical miles (1,720 kilometers) south of Honolulu, Hawaii. Kingman Reef is now administered and managed by the United States Fish and Wildlife Service, an agency of the United States Department of Interior. First known as "Dangerous Reef", Kingman Reef was discovered on June 14, 1798, by U.S. Captain Edmund Fanning.

Nineteenth century 1821 South Orkney Islands The South Orkney Islands are a group of islands in the Southern Ocean, about northeast of the tip of the Antarctic Peninsula. As part of the British Antarctic Territory, the islands have a total area of about . In December 1821, Captain Nathaniel B. Palmer as commander of the James Monroe, along with British sealer George Powell, co-discovered the South Orkney Islands.

1822 Howland Island Howland Island, a territory of the United States and a part of the United States Minor Outlying Islands, is an uninhabited coral island located just north of the equator in the central Pacific Ocean, about southwest of Honolulu, Hawaii. The island lies almost halfway between the U. S state of Hawaii and Australia. Its nearest neighbor is Baker Island, 37 nautical miles (68 kilometers) to the south. Now known as a National Wildlife Refuge, Howland Island is an insular area administered and managed by the United States Fish and Wildlife Service. First known as "Worth Island", Howland Island as it later was named, was discovered by U.S. Captain George B. Worth aboard the whaler Oena in 1822.

1825 Baker Island Baker Island, a territory of the United States and a part of the United States Minor Outlying Islands, is an uninhabited atoll located just north of the equator in the central Pacific Ocean about southwest of Honolulu, Hawaii. The island lies almost halfway between the U.S. state of Hawaii and Australia. Its nearest neighbor is Howland Island, 37 nautical miles (68 kilometers) to the north. Now known as a National Wildlife Refuge, Baker Island is an insular area administered and managed by the United States Fish and Wildlife Service. According to an article in Pacific Magazine dated in 2000, Baker island was reportedly first sighted in 1825 by U.S. Captain Obed Starbuck in the ship Lopez. The newly discovered island was named New Nantucket (and also as Phoebe). It was in 1832 that U.S. Captain Michael Baker, after whom the island is now named, also came to the island aboard the whaler Gideon Howard.

1831 Chloroform Chloroform is a chemical compound in the trihalomethane family that does not undergo combustion in air, although it will burn when mixed with more flammable substances. Chloroform was first discovered in July 1831 by American physician Samuel Guthrie, independently a few months later by French chemist Eugène Soubeiran and then by German chemist Justus von Liebig.

1858 Hadrosaurus foulki

Hadrosaurus was a dubious genus of a hadrosaurid dinosaur that lived near what is now the coast of New Jersey in the late Cretaceous, around 80 million years ago. It was likely bipedal for the purposes of running, but could use its forelegs to support itself while grazing. Like all hadrosaurids, Hadrosaurus was herbivorous. Its teeth suggest it ate twigs and leaves. In the summer of 1858 while vacationing in Haddonfield, New Jersey, William Parker Foulke discovered the world's first nearly-complete skeleton of any species of dinosaur, the Hadrosaurus (named by Joseph Leidy), an event that would rock the scientific world and forever change our view of natural history. To this day, Haddonfield, New Jersey is considered to be "ground zero" of dinosaur paleontology.

1859 Midway Atoll

Midway Atoll, better known as Midway Island or collectively as the Midway islands, is a territory of the United States and a part of the wider United States Minor Outlying Islands that is located in the North Pacific Ocean near the northwestern end of the Hawaiian Islands. As a 2.4-square-mile (6.2 km2) atoll, Midway Atoll is one-third of the way between Honolulu, Hawaii and Tokyo, Japan, approximately 140 nautical miles (259 kilometers) east of the International Date Line, about 2,800 nautical miles (5,200 kilometers) west of San Francisco, California, and 2,200 nautical miles (4,100 kilometers) east of Tokyo, Japan. Midway Atoll consists of a ring-shaped barrier reef and several sand islets. The two significant pieces of land, Sand Island and Eastern Island, provide habitat for millions of seabirds. Because of the importance of marine and biological environment, Midway Atoll is an insular area known as the Midway Atoll National Wildlife Refuge that is administered and managed by the United States Fish and Wildlife Service, an agency of the United States Department of Interior. Midway Atoll is perhaps best known as the site of the Battle of Midway, fought in World War II on June 4–6, 1942 and the decisive turning point of the Pacific War when the United States Navy defeated an attack by the Empire of Japan. First known as "Middlebrooks Islands", Midway Atoll was discovered by U.S. Captain N.C. Brooks aboard his ship, Gambia, on July 8, 1859.

1859 Petroleum jelly

Petroleum jelly, petrolatum or soft paraffin is a semi-solid mixture of hydrocarbons originally promoted as a topical ointment for its healing properties. The raw material for petroleum jelly was discovered in 1859 by Robert Chesebrough, a chemist from New York. In 1870, this product was branded as Vaseline Petroleum Jelly.

1873 Chemical potential