Principia Astronomical Observatory

The Principia College Historic District is a National Historic Landmark District encompassing the central portion of the campus of Principia College in Elsah, Illinois. The campus master plan, as well as eleven of its buildings, are important late designs of architect Bernard Maybeck, best known for his influential architecture in the American West. The Principia was declared a National Historic Landmark in 1993, and was also placed on the National Register of Historic Places that same year.

Principia College is a private liberal arts college in Elsah, Illinois. It was founded in 1912 by Mary Kimball Morgan with the purpose of "serving the Cause of Christian Science." "Although the College is not affiliated with the Christian Science Church, the practice of Christian Science is the cornerstone of campus life." Principia sits on bluffs overlooking the Mississippi River between Alton and Grafton in the Metro East region of Southern Illinois, thirty miles north of St. Louis. A portion of the school's 2,500-acre (1,000 ha) campus is a designated National Historic Landmark District, for its many buildings and design by architect Bernard Maybeck.

Elsah is a village in Jersey County, Illinois. As of the 2020 census, the village had a total population of 519. Michael Pitchford is the village's current acting mayor. It is the home of Principia College. Elsah is a part of the Metro-East region and the St. Louis Metropolitan Statistical Area.

The Elsah Historic District is a 350-acre (140 ha) historic district in Elsah, Illinois. The district includes 48 contributing buildings which reflect the village's period of growth in the 1850s. Elsah was founded in 1853 as a riverfront town on the Mississippi River; by 1861, it had grown to its current size, as geographic and economic limitations prevented further expansion. The town's 1861 appearance is well-preserved, and three distinct areas of the town have gone almost entirely unchanged since. The historic commercial district on LaSalle Street, which extends three blocks inward from the river, consists mainly of stone buildings; all but one of its pre-1861 buildings, including all four of the village's historic taverns, still stand. The other two districts are both located on Mill Street and are primarily residential; the larger one is three blocks long and has an assortment of stone and brick houses, while the smaller section has a single block of Greek Revival homes. The district was added to the National Register of Historic Places on July 27, 1973.

Beltrees is an unincorporated community in southern Jersey County, Illinois, United States. Beltrees is 2 miles (3.2 km) east-northeast of Elsah.

Elsah Township is one of eleven townships in Jersey County, Illinois, United States. As of the 2010 census, its population was 2,462 and it contained 1,027 housing units.

Portage Des Sioux is a city in St. Charles County, Missouri, United States. The town sits on the Mississippi River roughly opposite Elsah, Illinois, and is the home of the riverside shrine of Our Lady of the Rivers. The population was 328 at the 2010 census. The city was founded in 1799 by Spanish Lt. Gov. Zenon Trudeau and François Saucier in reaction to American plans to build a military post about twelve miles (19 km) downstream. The French name derives from the overland escape route between the Missouri River and Mississippi River used by a band of Sioux, fleeing enemies; they used this area as a portage for their canoes, outdistancing their rivals who instead paddled all of the way to the confluence of the rivers. The Treaties of Portage des Sioux in 1815 were signed here ostensibly settling Native American and United States conflicts in the War of 1812. The treaties consolidated and affirmed the Treaty of St. Louis (1804) in which the Sac and Fox ceding northeast Missouri and much of Illinois and Wisconsin and the 1808 Treaty of Fort Clark in which the Osage Nation ceded all of Missouri and Arkansas. These treaties were to ultimately result in the Black Hawk War and the tribes being forced to move west of Missouri.

Chautauqua is a populated place in Jersey County, Illinois. Also known as the New Piasa Chautauqua Historic District which is a private semi-gated summer resort that started as a 19th-century tent settlement. The name Piasa is taken from a nearby Native American painting of a mythical bird, called the Piasa Bird, which was painted on the bluffs high above the Mississippi River. Chautauqua is located between Elsah and Grafton in Jersey County. Today, it is bordered by and has access from the Great River Road (Illinois Route 100). It has functioned as a private non-denominational Christian summer resort for over a century.

Machens is an extinct town in St. Charles County, in the U.S. state of Missouri. The GNIS classifies it as a populated place. The eastern end of the Katy Trail, a recreational rail trail, is located at Machens.A post office called Machens was established in 1895, and remained in operation until 1956. The community most likely was named after Andrew Machens, Sr.

The River Bend is a small region in western central Illinois and southern Illinois that comprises parts of Madison County and Jersey County. The name comes from a section of the Mississippi River that flows roughly west to east instead of the usual north to south, causing a bend in the river. The area is within the Metro East region, which is within the Greater St. Louis Metropolitan area. The western boundary is dictated by the flow of the Mississippi river, beginning at the confluence of the Illinois and ending at the confluence of the Missouri. The eastern boundary stretches through a contiguous urbanized area revolving around the cities of Alton and Wood River.