Geographically, Incheon is located approximately 126° 37'E and 37° 28'N, which puts it at the heart of the Korean peninsula. Most notably, Incheon is located downstream of Hangang River, and its shoreline faces the Yellow Sea. Located 28km from Seoul, the capital of South Korea, Incheon is similar to cities such as San Francisco, Washington, and Madrid in terms of latitude.

Although Incheon has a continental climate, it does enjoy some elements of an oceanic climate given its proximity to the sea (e.g. relatively more stable annual temperature range compared to other inland areas). The annual average temperature hovers around 12.1℃ - all-time high temperature was 38.9℃ (recorded on August 16, 1949), all-time low temperature was -21.0℃ (January 11, 1931). Incheon receives roughly 1,234.4mm in annual precipitation, which is less than other areas at similar latitudes. Annual average wind speed is 2.9m/s, which mainly blows in from the north-northwest, and from the north or northwest to a lesser degree. Wind speed picks up the most between February and April, and dies down in September. Incheon is prone to long stretches of what is known as the "Yellow Dust" phenomenon. High pressure in central China pushes sand and dust from mainland China towards the Korean peninsula. Combined with heavy fog generated from the Yellow Sea, yellow dust often leads to lower daytime temperatures. In total, Incheon has 49.4 fog days, of which 64% occur between April and July.

When Incheon was reclassified as a directly controlled city on July 1, 1981, its total area stood at 201.21km². On January 1, 1982, Incheon's total footprint grew to 310.83km² following the incorporation of Gyeyang-myeon in Gimpo-gun, Gyeonggi-do (30.9km²) and Yeongjong/Yongyu-myeon in Ongjin-gun, Gyeonggi-do (72.0km²) into Incheon. After Incheon's reclassification as a metropolitan city (January 1, 1995), on March 1, 1995, Ganghwa-gun (401.3km²), Ongjin-gun (163.6km²), and Geomdan-myeon in Gimpo-gun (42.2km²) were further incorporated into Incheon, bringing the city's total area to 955km². Incheon has continued to grow since the turn of the century through land reclamation projects on public waters. In 2005, Incheon was measured at 994.12km², reaching 1% of the total area of Korea. As of December 31, 2022, Incheon stretches across a total area of 1,067.04km².

Except for a dozen or so mountains, including Manisan Mountain (469m), Gyeyangsan Mountain (395m), and Samgaksan Mountain (343m), most of Incheon sits below 300m above sea level. As such, there are no major rivers originating from Incheon and its surrounding areas. Some smaller rivers such as Gulpocheon, Cheongcheoncheon, and Gyesancheon flow into Hangang River, while others such as Sicheoncheon and Gongconcheon to the north and Seunggicheon, Mansucheon, Jangsucheon, and Unyeoncheon to the south drain into the Yellow Sea. All rivers, except Gulpocheon (11.5km), are less than 10km in total length - e.g. Seunggicheon (6.2km), Geomdancheon (6.74km). Incheon has a rias coastline, which means it has a long and complicated shoreline with plenty of islands. More specifically, Incheon has 168 islands in total, 128 of which are deserted islands with no inhabitants.

Past and present projects have helped Incheon grow and develop into the bona fide international city it is today - Incheon Harbor and Incheon subway development project (October 1999); Incheon International Airport project (March 2001); land reclamation projects on public waters; various industrial and logistics facilities development projects; tourism/leisure facilities and housing complex development projects; highway expansion projects; education/culture facilities development projects; Songdo New Town development project and Free Economic Zone Authority (October 2003), Incheon Daegyo Bridge construction project (October 2009); Successful execution of the 2014 Asian Games, etc. Propelled by these projects, Incheon continues to grow today.