At the 2011 census, there were 121,308 inhabitants in the metropolitan area of Cayenne (as defined by INSEE),[3] 57,229 of whom lived in the city (commune) of Cayenne proper.

Cayenne is located on the banks of the estuary of the Cayenne River on the Atlantic Ocean. The city occupies part of the Ile de Cayenne. It is located 268 km from Saint-Laurent-du-Maroni and 64 km from Kourou.

Paris: 7,100 kilometres (4,400 mi).

Fort-de-France, capital of Martinique: 1,500 kilometres (930 mi).

Paramaribo, capital of Suriname: 342 kilometres (213 mi) to the northwest.

Macapá, capital of the state of Amapá, Brazil: 554 kilometres (344 mi) to the southeast.

Ignored by Spanish explorers, who found the region too hot and poor to be claimed, the region was not colonized until 1604, when a French settlement was founded. However, it was soon destroyed by the Portuguese, who were determined to enforce the provisions of the Treaty of Tordesillas. French colonists returned in 1643 and founded Cayenne, but they were forced to leave once more following Amerindian attacks.

 In 1664, France finally succeeded at establishing a permanent settlement at Cayenne. Over the next decade the colony changed hands between the French, Dutch, and English, before being restored to France. It was captured by an Anglo-Portuguese force at the invasion of Cayenne in 1809 and administered from Brazil until 1814, when it was returned to French control. It was used as a French penal colony from 1854 to 1938.

The city's population has recently grown dramatically, owing to high levels of immigration (chiefly from the West Indies and Brazil) as well as a high birthrate.

Cayenne is very ethnically diverse, with Creole, Haitian, Brazilian, European, and Hmong and other Asian communities. It is famous for its annual carnival which starts with the arrival of Vaval (the Carnival King) on the first Sunday after New Year's Day and continues with very popular all-night costume balls and Sunday afternoon parades every weekend until Mardi Gras.

 Carnaval dances include mazurka, biguine and piké djouk. It is the role of the Touloulou (disguised woman) to invite men to dance; the men do not have the right to refuse her. Only Touloulou have the right to dance, non-disguised women may not dance.

There is a large dance scene including both lessons and social dancing. Cafe de la Gare and Domino offer a variety of opportunities including bachata, salsa, merengue, kizomba, zouk, and forro. There are occasionally outdoor socials nears the Place de Chaînes Brisées. Capoeira is also popular and is offered in multiple styles by groups such as ENERGIA PURA.

Cayenne Cathedral is the seat of the Roman Catholic Diocese of Cayenne

Cayenne centres on its main commercial street, the Avenue Général de Gaulle. At the east end of the avenue near the coast is the Place des Palmistes and the Place de Grenoble (also known as the Place Léopold Héder). 

Most of the official buildings are located in this area: the Hôtel de Ville (the town hall) built by Jesuits in the 1890s, the Post Office, the Préfecture, residence of French Guiana's Préfect, and the Musée Départmental Franconie. 

To the west of this area lies Fort Cépérou, built in the 17th century, though now mostly in ruins. To the south lie the Place du Coq and Place Victor Schoelcher (named in honour of the anti-slavery activist) and a market.

To the south of this compact region is the Village Chinois (known as Chicago), separated from the rest of Cayenne by the Canal Laussat. It has a reputation for being a dangerous area.

Other buildings in the city include Cayenne Cathedral, municipal library, the municipal museum and a museum of French Guianese Culture (Musée des Cultures Guyanaise) and a scientific research institute (IRD or Institut de recherche pour le développement, formerly Orstom). The Jardin botanique de Cayenne is the city's botanical garden.

Under the Köppen climate classification, Cayenne has a tropical monsoon climate. Average high and low temperatures are nearly identical throughout the course of the year averaging about 30 °C (86 °F) and 23 °C (73 °F) respectively. Cayenne sees a copious amount of precipitation during the year. The city features a very lengthy wet season and a very short dry season. 

The dry season only covers two months of the year (September and October) while the wet season covers the remainder of the year. Precipitation is seen even during the dry season, a trait commonly seen in places featuring tropical monsoon climates. Cayenne averages roughly 3,750 millimetres (150 in) of rain each year.