Sussex straddles the Kennebecasis River, 70 km (43 mi) northeast of Saint John, and is a major dairy product producer in the province.

[citation needed] In 1857, the European and North American Railway was opened, connecting the farming communities of the Kennebecasis River valley with Saint John and Moncton.

The settlers were for the most part British Loyalists who had fled the American Revolution in 1776, with many Irish refugees of the Great Famine from the mid-19th century settling in the nearby farming communities.

In the early 1960s, several local roads were upgraded as part of the Trans-Canada Highway project which saw Route 2 pass immediately north of the town between Fredericton and Moncton.

At the same time, a series of local roads in the Kennebecasis River valley were designated as Route 1, running from an interchange with the Trans-Canada at Sussex, southwest to Saint John.

The creation of Sussex as a highway interchange in this post-war period led to some transportation planners in New Brunswick calling for the consolidation or closure of the Fredericton, Saint John and Moncton airports to be replaced by a single airport located in Sussex to serve all three population centres of southern New Brunswick; this was before the facilities underwent considerable expansion in the late 1950s to early 1960s.

[7] Sussex also began to see a growing tourism trade, with many flocking to see the collection of wood-constructed covered bridges throughout the central area of Kings County.

[10] The town entered economic difficulty during the late 1990s after the Cassidy Lake potash mine flooded, resulting in hundreds of lay-offs.

Another significant blow came in October 2002 with a realignment of the Trans-Canada Highway (Route 2) between Fredericton and Moncton which no longer passed through Sussex, instead carrying the province's east–west interprovincial traffic 30 km (19 mi) north of the town.

In 2022, there were rumours that the regional potash mines might reopen, due to a substantial rise in the market price of the commodity; however, Nutrien declined to do so.

[12] The town plays host to a handful of radio stations: The largest hot air balloon festival in Atlantic Canada is held each summer in Sussex.

Located in Sussex, this facility is the host of many shows that include equine, dogs, livestock, sales and exhibitions as well as 4H and youth group activities.