Smithfield was the westernmost freight port on the Neuse River, and in 1770 the colonial government erected a tobacco warehouse there to store the crop before it was shipped out.

Production for sale at markets remained low before the 1850s due to poor transportation links with other parts of the state.

In 1856 the North Carolina Railroad was completed, connecting Johnston County with major urban areas.

As result, farming for sale increased, lumber and turpentine industries developed, and the towns of Princeton, Pine Level, Selma, and Clayton were eventually created.

[9] In 1886 the "Short-Cut" line of the Wilmington and Weldon Railroad was laid through Johnston, eventually giving rise to the towns of Kenly, Micro, Four Oaks, and Benson.

[10] The Panic of 1893 caused cotton prices to sharply decline, leading area farmers to switch to bright leaf tobacco as their primary cash crop.

[12] While local commerce enjoyed significant success during the decade, area farmers struggled due to drops in tobacco and cotton prices.

The Wall Street Crash of 1929 and ensuing Great Depression caused all banks in the county close.

The commissioners enact policies such as establishment of the property tax rate, regulation of land use and zoning outside municipal jurisdictions, and adoption of the annual budget.

However, from 1968 onward it has turned increasingly Republican, with the only breaks in this tradition being its support for third-party candidate George Wallace in 1968 and for Democrat Jimmy Carter in 1976.

Carter's unsuccessful bid for reelection in 1980 is the last time that a Democrat has managed even 40 percent of the county's vote.

In the 2020 North Carolina gubernatorial election, Republican Dan Forest won the county by a 17% margin over Democrat Roy Cooper.

The Battle of Bentonville was fought in 1865, and was the only Confederate offensive targeted to stop General Sherman's march through the South.

The Tobacco Farm Life Museum in Kenly has been collecting artifacts and showcasing the heritage of the Eastern North Carolina farmer for over 35 years.

[40] Johnston County is located in the Raleigh-Durham radio market, ranked by Nielsen as the 37th largest in the United States.

[41] The county is also home to WPYB, 1130 AM in Benson, WHPY, 1590 AM in Clayton, WTSB, 1090 AM in Selma, and WKJO, 102.3 FM in Smithfield.

WNGT-CD, (virtual channel 34.1) a Class A low-powered TV station licensed to both Smithfield and Selma.