As of October 1, 2016, the city has an estimated population of 53,258 and a population density of 99 persons per km2. The total area is 536.12 km2.
Nichinan is on Japan's southernmost main island, Kyūshū. The average annual temperature is 18.7 degrees Celsius with average annual rainfall of 2573.5 ml.
Mandarin oranges, ponkan, sweet peas, green peppers, kumquats, and rice are the main agricultural products of Nichinan, a sector that employs 2,130 people. In addition, logging, particularly of obi cedar, takes place on 3,451 hectares of land. Fishing of tuna, bonito, and spiny lobster is another major industry.
Manufacturing is worth approximately ¥47.2 billion per year. Tourism draws over a million visitors each year.
Nichinan began as part of the Fujiwara Shōen in the Heian period. The city's history and development were heavily influenced by the history of Obi town, a district of Nichinan which still exists today. Obi was one of the eight districts of Hyūga, an old province in eastern Japan, which was ruled by the Itō clan based at Obi Castle.
Throughout the Sengoku period, the Itō clan's most serious rival was the neighbouring Shimazu clan. The Shimazu clan had unified Satsuma Province and Ōsumi Province under its control, and began to clash with the Itō clan in 1570. The Itō clan was finally defeated by the Shimazu clan in 1578. After seeking help from then Shōgun Toyotomi Hideyoshi, the family's lands were restored in 1587 after his invasion of Kyūshū and subjugation of the Shimazu clan. By the Edo Era, the Itō clan regained its holdings, which came to be known as the Obi Domain. In the period after the Edo period, efforts were poured into quality education at the Shintoku Clan School in Obi. The school is where the Meiji period diplomat Marquis Komura Jutarō graduated from.
On January 1, 1950, the city was established through an amalgamation of Agata town, Aburatsu town, Obi town, and Togo village. On February 1, 1955, Futo village and Hosoda town joined the city district. The current Nichinan city was established on April 1, 1956, when it amalgamated with Sakatani village, Kahara village, and the Odotsu district. Since 1963, Nichinan has been the spring training location for the Hiroshima Carp baseball team.
In 1998, plans were made to extend the eastern Kyūshū expressway to come as far as Kitagō town and Nichinan. In 1999, a 12-meter wharf was completed at the eastern head of Aburatsu port. Aburatsu's increasing role as a harbor has made it a regular stopover for both domestic and foreign ships, and it is becoming an authentic international trading port. From 2001 to 2010, a general plan for the future of Nichinan was drawn up, with the simple theme of progressing Nichinan as, "a city that combines its fragrant history and culture with the sunshine and lush green mountains."
During the nationwide round of Heisei-era mergers, the Nichinan-Kitagō-Nangō Merger Association (日南市・北郷町・南郷町合併協議会, Nichinan-shi-Kitagō-chō-Nangō-chō Gappei Kyōgikai) was formed in August 2004 by the area's residents to consider the merger of the three municipalities. The group was, however, dissolved in May 2005 when the Kitagō Town Council vetoed the proposed merger bill despite the support for the merger by residents in both Kitagō and Nangō towns. The association was reconstituted on September 28, 2007, when merger supporters in both towns gained majorities on their respective town councils. On March 30, 2009, the three municipalities agreed to merge and become the new city of Nichinan.
There are three major festivals that occur in Nichinan throughout the year:
Other events include spring and autumn training for the Hiroshima Carp baseball team, various swimming and marathon events, and monthly morning markets held at Aburatsu port and in front of Nichinan City Hall.
Other points of interest include:
JR Kyūshū provides rail transport through the city via the Nichinan Line. The city's central station is Nichinan, but Aburatsu and Obi provide access to their respective districts.
National Route 220 is the main transportation artery, passing through the center of the city. National Routes 222 and 448 also provide automobile access through the city.
There are seven kindergartens, 14 elementary schools, 11 junior high schools, and three high schools located within the city.