Demerara (/ˌdɛməˈrɛərə/; Dutch: Demerary, [ˌdeːməˈraːri]) is a historical region in the Guianas, on the north coast of South America, now part of the country of Guyana. It was a colony of the Dutch West India Company between 1745 and 1792 and a colony of the Dutch state from 1792 until 1815. It was merged with Essequibo in 1812 by the British who took control. It formally became a British colony in 1815 until Demerara-Essequibo was merged with Berbice to form the colony of British Guiana in 1831. In 1838, it became a county of British Guiana until 1958. In 1966, British Guiana gained independence as Guyana and in 1970 it became a republic as the Co-operative Republic of Guyana. It was located around the lower course of the Demerara River, and its main settlement was Georgetown.

The name "Demerara" comes from a variant of the Arawak word immenary or dumaruni, which means "river of the letter wood" (wood of Brosimum guianense tree). Demerara sugar is so named because originally, it came from sugarcane fields in the colony of Demerara.

Demerara was first mentioned in 1691 as a trading post. On 18 October 1745, Demerara was created as a separate colony, even though it was located on an unoccupied part of Essequibo, because the people from the province of Holland wanted to settle there and Essequibo was part of Zeeland. In the founding documents, it was mentioned that the colonists should live in peace with the Amerindian population and respect their territories, because they fought with the colony of Essequibo against the French privateers and helped to chase them off. The Amerindians were considered free people, and they were not allowed to enslave them.

The first planter was Andries Pieterse who already owned a plantation in Essequibo. Half a year later, there were 18 large sugar plantations and 50 smaller plantations. The colony was initially governed from Fort Zeelandia by Laurens Storm van 's Gravesande, the governor of Essequibo. In 1750 he appointed his son Jonathan as Commander of Demerara.

Demerara grew rapidly, and attracted many English planters. The Dutch West India Company, who had a monopoly on the slave trade, was unable to supply them, leading to illegal smuggling from English colonies.

In 1755, Gedney Clarke, a Barbados merchant and plantation owner, requested political representation, therefore the administration was moved to the island of Borsselen, 20 miles (32 km) upriver near plantation Soesdyke which was owned by the commander of Demerara. The decision was criticised because the island was hard to defend, and the planters had started to build houses around the guard post near the mouth of the river. That settlement later became known as Stabroek, and in 1782 the capital of the colony. The town was renamed Georgetown in 1812.

In 1763, a slave uprising took place in neighbouring Berbice. Governor van 's Gravesande formed an alliance with the Amerindian Arawak, Kalina, Warao and Akawaio tribes, and prevented the uprising from spreading to Demerara and Essequibo. 50 soldiers from Demarara were sent to Berbice as assistance. The slave uprisings were a source of concern: in a 1767 letter to Frederick the Great, the King of Prussia, which aimed to promote the colony for German planters, a request was added for 100 soldiers.

In 1780, there were almost 200 plantations in Demerara compared to 129 in Essequibo. Demerara had become more successful than Essequibo. The rivalry between the colonies resulted in the creation of a combined Court of Policy in Fort Zeelandia. The majority of the white population of the colony were English and Scottish planters.