Jefferson County

Administrative district of north-central Alabama; area 2,898 sq km/1,119 sq mi, population (1990) 651,500. Jefferson County is Alabama's most populous county, and is dominated by the city of Birmingham, where the county has its seat.

The suburbs of Birmingham occupy much of the eastern half of Jefferson County. Bankhead Lake, on the Black Warrior River, forms part of its western boundary. The region's wealth is based on a combination of iron ore in the mineral belt in the south of the county and coalmines in the north.

Jefferson County

Administrative district of central Colorado; area 1,989 sq km/768 sq mi, population (1990) 438,400. In the southeast, the county is bounded by the South Platte River, and it has its seat at Golden.

The rapidly growing northeastern part of Jefferson County contains several suburbs of Denver, such as Arvada, Lakewood, and Wheat Ridge. The agricultural areas of the county produce sugar beets, beans, and livestock. Its western section includes parts of Arapahoe, Pike, and Roosevelt national forests, as well as part of the Front Range of the Rocky Mountains, where there is some coalmining.

Jefferson County

Administrative district of north-central Kentucky; area 1,000 sq km/386 sq mi, population (1990) 664,900. Its seat is at Louisville, the state's largest city.

Jefferson County is bordered on the northwest by the Ohio River and the state of Indiana. The metropolitan area around Louisville is the site of residential suburbs and of much of the state's manufacturing. In the outlying, rural parts of the county a variety of crops are grown (onions, potatoes, burley tobacco, grain, and fruit), and livestock are raised.

Jefferson County

Administrative district of east-central Missouri; area 1,712 sq km/661 sq mi, population (1990) 171,400. Its seat is at Hillsboro (population 1,625), and it is bounded on the east by the Mississippi River, which forms the border with Illinois.

The northeastern part of Jefferson County is home to several of the southern residential and industrial suburbs of St Louis, which have grown enormously since the 1970s. These cities close to the Mississippi, particularly Festus, contain much of the county's manufacturing base. Jefferson County also produces livestock and cereals, while lead and zinc deposits are exploited in the south.

Jefferson County

Administrative district of northern New York State; area 3,297 sq km/1,273 sq mi, population (1990) 110,900. Its seat is at the major industrial centre of Watertown.

Jefferson County is bounded on the west by Lake Ontario, and on the northwest by the St Lawrence River and the Canadian border. It includes several of the Thousand Islands in the Gulf of St Lawrence, and Fort Drum occupies the northeast part. There are numerous dairy farms here, and commercial fishing is important. Iron, limestone, and talc are also mined. The county contains many lakeside resorts and state parks.

Jefferson County

Administrative district of eastern Ohio; area 1,062 sq km/410 sq mi, population (1990) 80,300. Its seat and principal city is Steubenville, a manufacturing centre particularly known for its steel and other metals.

Jefferson County is bounded on the east by the Ohio River, which forms the border with West Virginia. Coalmining is an important economic activity in the county, and there is also a variety of farming (dairy, fruit, livestock, and market garden produce).