Lambton County started as a part of the District of Hesse. The district of Hesse included British territories west of Long Point, (practically all of western Ontario). The district was latter divided and renamed using English district names (Essex, Sulfolk, Kent, etc). Lambton was part of Kent county. In 1849 districts were abolished and the County of Lambton was formed. Lambton and Kent first shared the capital city of Sandwich (since renamed as Windsor, Ontario). In 1852 the partnership was devolved and Lambton become of full county. It is named in honour of the Earl of Durham who lived in Lambton Castle. (Source: London Free Press, July 15, 1939, by W.G. Trestain)
The largest city in Lambton County is Sarnia, which is located at the mouth of the St. Clair River. The two Blue Water Bridges cross the river at Sarnia, connecting it to Port Huron, Michigan. The bridges are one of the busiest border crossings between the two countries. The river is also traversed by two passenger ferries further south, and a rail tunnel, also at Sarnia, runs underneath it.
Today, the petrochemical industry is arguably the most important sector of Lambton County's economy. Established during World War II, Sarnia and the area along the St. Clair River is home to a major processing centre for oil from Alberta. Lambton County is the site of North America's first drilled commercial oil well at Oil Springs, Ontario in 1858. Now, the petrochemical industry is so pervasive that it has earned this region along the river the nickname "Chemical Valley". Often the moniker is used after a chemical spill into the river or a day of extreme air pollution.
Tourism is another important industry in Lambton County, especially along the lake and river. The community of Grand Bend, and the Pinery Provincial Park are especially popular tourist destinations, attracting thousands of people each week throughout the summer to their long, uninterrupted beaches. The part of Lambton County along Lake Huron known as Lambton Shores depends almost entirely upon the seasonal industries of tourism and agriculture for its well-being. There are also popular conservation areas along the St. Clair River, and a conservation area named Rock Glen Falls near Arkona along the Ausauble River internationally known for its Devonian Era fossils.
Though no longer as important to the county's economy, agriculture is still what sustains many small towns in the interior of Lambton County. The three most popular crops are corn, wheat, and soybeans, although canola and sugar beets (among other things) are sometimes planted. Many farmers raise cattle in addition to growing crops.