Иллинойс штатының Джефферсон округі

County in Illinois, United States

Jefferson County is a county located in the southern part of the U. S. state of Illinois. According to the 2020 census, it has a population of 37,113. The county seat is Mount Vernon. Jefferson County contains the Mount Vernon, Illinois micropolitan area. It is located in the southern portion known locally as "Little Egypt". The western border of the county adjoins the Greater St. Louis consolidated metropolitan statistical area, the Metro East region, and the St. Louis commuter region and market and viewing area.

The first settler in Jefferson County is believed to have been Andrew Moore. In 1810, he settled near the southeast corner of the county, near where the Goshen Road emerges from the forest of Hamilton County into what is now known as Moore's Prairie. Moore arrived from the Goshen Settlement, near Edwardsville. His migration was therefore retrograde, from the west toward the interior of the State. In 1814, Andrew Moore departed with his eight year old son for Jordan's settlement, a journey from which he never returned. A skull that was believed to have been Moore's was found several years later about two miles from his cabin. Jordan's Settlement, also called Jordan's Fort, was southeast of modern Thompsonville, Illinois, about twenty miles south of Moore's cabin. This episode occurred during the War of 1812 when many of the Indian tribes were allied with the British. In 1816, Carter Wilkey, Daniel Crenshaw and Robert Cook settled in Moore's Prairie. Daniel Crenshaw moved into Moore's cabin. This settlement is believed to be the first permanent settlement in the county. Jefferson County was organized in 1819, out of parts of White, Edwards and Franklin Counties. It was named in honor of Thomas Jefferson, principal draftsman of the Northwest Ordinance, among other things. The baseline along the northern border of the County crosses the Third Principal Meridian at the northwest corner of the county.

In 2015 the county police department announced that the words "In God We Trust" will be on police squad cars. Jeff Bullard is the current Sheriff of Jefferson County.