Founded in 1856, DeKalb became important in the development and manufacture of barbed wire, especially for agriculture and raising livestock.

[4] The name is for Baron Johann de Kalb, a major general in the American Revolutionary War.

Joseph Glidden (1813–1906), a DeKalb resident since about 1850, received a patent in 1874 for inventing the conventional double-strand barbed wire that remains in common use around the world today.

Between 1892 and 1898 Glidden and Ellwood played substantial parts in establishing the state teachers college that became Northern Illinois University.

[6]: 46–49  From a base in the early county Farm Bureau, the DeKalb Agricultural Association produced large quantities of high-yield seed varieties, beginning in 1934.

A series of joint ventures and mergers beginning in 1982 resulted in the DeKalb brand of agricultural products being owned by Bayer since 2017.

Precipitation is somewhat uniform year-round, although it can be heavier in the spring and summer when the area is prone to strong thunderstorms.

[14] In 2011, DeKalb was the broadcast base of Up and In: The Baseball Prospectus Podcast with Kevin Goldstein and Jason Parks.

In June, 2020, Meta announced it would construct an $800 million data center on the south side of DeKalb.

Members of the League of Women Voters established the park district in 1935 to address the need for a public swimming pool.

The park district provides year-round athletic and recreation programs including day camps, youth baseball and softball, adult softball leagues both indoors and outdoors, swimming lessons, golf lessons, karate, tennis, adult and youth basketball leagues, indoor soccer, fitness classes, and preschool.

Since 2006, the nearest passenger rail service is at the Metra commuter system station in Elburn, 15 miles (24 km) east of DeKalb, which is accessible by bus.

In January 2023, the Dekalb City Council voted to fund a transportation study aimed at determining feasibility of extending Metra Union Pacific West Line commuter rail service from Elburn to the city.

Interstate Highway 88, part of the Illinois Tollway system, was completed to DeKalb around 1975 and passes just south of town, where there are two toll plazas and a service oasis that includes restaurants and a gas station.

[26] Routes extend through the university, the city, and Sycamore with extensions west to Kishwaukee College and east to the passenger rail station at Elburn.

The system began in 1971 as the Huskie Bus Line under contract to the NIU Student Association.

[28] By 1982 the system served 3 million riders per year, second only in Illinois to the Chicago Transit Authority.

In 2018, it merged with a smaller City of DeKalb bus system, which had been operated by the local Voluntary Action Center (VAC).

[30] VAC continues to serve a wider surrounding area with on-demand transportation for people with special needs and to out-of-town medical appointments.

[31] DeKalb Taylor Municipal Airport (DTMA) (ICAO: KDKB, FAA LID: DKB), serving the general aviation community, is on the east side of the city at 3232 Pleasant Street.

The airport opened in April 1944 in association with a factory making Interstate TDR assault drone aircraft.