From 1734 to 1735, court was held at "the court house on New River." In 1735, it was held at Joseph Howard's, and at Christian Heidleber's. After April, 1737, it was held at "the court house on New River." That courthouse was burned in 1744. Between 1744 and 1753, court was held at "Johnston on New River." Johnston was established in 1741. For a while, court was held at the private homes of James Foyle and Thomas Black. In 1753, the court met at Jonathan Melton's on North East New River, a storm having destroyed Johnston in 1752. In 1757, court was held at the new courthouse at Wantland's Ferry on New River. In 1819, a new courthouse was authorized to be established within one-half mile from the old courthouse and on the same side of the river. In 1842, Jacksonville was authorized, but it was not laid out until after 1849. It became the county seat from that time forward.

Onslow County was formed in 1731 from New Hanover County and was named for Sir Arthur Onslow, speaker of the House of Commons in the British Parliament. Records in the Register of Deeds office at the Onslow County Courthouse date back to 1713.

The first settlers of Onslow County were three English men who came in 1705, to Town Point on the New River. Those men were William Brown, Thomas Warren, and Thomas Worsley. They were settled for six years before they were joined by a Frenchman, John Nasague, who settled on the Northwest branch of the New River. In the next eighteen years, 35 more families settled in the area.

J. Parsons Brown, the late Onslow County historian, says Onslow was established in 1731. On May 23, 1731, the royal council received a petition praying for a new precinct and an order of Governor George Burrington and his council, dated December 4, 1731, at Edenton, granted the request.

The Assembly protested the setting up of the county. Onslow delegates were not seated until a special act was passed by the Assembly on March 2, 1735, which "confirmed and established" the precinct of Onslow.

Court was held first at Courthouse Bay. In 1741, the Assembly authorized the establishment of the county seat at old Town Point, "to be known as Johnston" in honor of Governor Gabriel Johnston. Johnston town was decimated by an historic hurricane in 1752. Many records were lost. The county seat was then moved to its present site, but was then called Wantland's Ferry. The name was changed to Jacksonville in honor of Andrew Jackson in 1842.

The New River is the only river in North Carolina that begins and ends in the same county. It is also the widest river for its length in the state. Noting the distinctive character of the river, Onslow County's proximity to the Atlantic Ocean, its abundance of vegetation, fish and wildlife, and its topography provided an ideal area for settlement and moreover, provided an atmosphere conducive for growth and development.

Covering Onslow County, as her first settlers began to make their homes in the area, was the long leafed pine. This towering evergreen provided the first major cash crop in the area, turpentine. The turpentine provided by the long leaf pine was used to produce naval stores for the ship building industry, important to the colonies and England. These stands of timber also produced lumber for the area. Although the naval stores industry waned after the Civil War, the lumbering industry has remained strong in Onslow with $27,132.900 added to the economy in most recent times. A formidable feature of the county is Hoffmann Forest which consist of 78,000 acrea. The "teaching" forest was established by Dr. Julius Hoffmann of North Carolina State Univeristy. This site is also an outstanding representation of the welands of this area.

Vast wetlands, forest, game, and the scenic New River were also keys in expanding the economic endeavors of the county during the years between World War I and II. The 1930s was a period of tremendous growth for the recreation industry in Onslow County. Numerous rod and gun clubs were established, attracting members from the Piedmont, as well as out of state. One of those attracted to Onslow was Dr. William Sharpe. Dr. Sharpe purchased an area known as the Hammocks. This property eventually became the property of the state to be used as Hammocks Beach State Park. As a state part the area is a protected site and is well known for its protection of the sea turtle and its nesting area.

The recreation industry boom of the 1930s and 40s was short-lived following the outbreak of World War II. However, Onslow County's location and topography was instrumental in attracting the U.S. Government, which in turn established several military bases in the area, including the Camp Lejeune Marine Corps Base and the Camp Davis Army Training Base. Established for 50 years, Camp Lejeune now encompasses over one-third of the county's acreage of 111,000 acres. Camp Davis was closed in 1944. Camp Lejeune is also a haven for the red-cockaded woodpecker, which is on the endngered species list.

Once again Onslow County's location has worked to its advantage, creating a strong tourism industry and recreational environment for locals. With the Atlantic Ocean to its eastern border, recreational enthusiasts have numerous opportunities. Hours can be spent under the summer sun in playful pursuits such as water skiing, sailing, canoeing, and windsurfing. Pier fishing along with deep sea fishing trips provide further enjoyment. With its mild climate, the golf enthusiasts can enjoy five different courses within the boundaries of the county. Wildlife such as deer, bear, turkey, quail, rabbits, and dove can be found hunted by gun or the zoom lens of avid photographers.

Onslow has historically been a rural county and still is to a large degree. Most recent problems associated with the environment are becoming more complex because of the rapid growth of the urban population. Water and sewer problems along the potential development of land near wetlands are a major concern.

Parts of Onslow still remain heavily agricultural with major commodities including tobacco, corn, soybeans, swine and poultry taking the lead within the farm communities. Cotton a former cash crop is also enjoying a revival in the area. Commercial fishing also contributes significantly to the economy along with non-traditional agricultural interests such as ornamental horticulture, commercial horticulture, and aquaculture.