St. Croix County is a county in the U.S. state of Wisconsin. As of 2010, the population was 84,345. Its county seat is Hudson. St. Croix County is part of the Minneapolis–St. Paul Metropolitan Statistical Area (MSA). It is the fastest growing county in Wisconsin.
St. Croix County was created on August 3, 1840 by the legislature of the Wisconsin Territory. It was named after the river on its western border. Sources vary on the origin of the name; the St. Croix River may have been named after Monsieur St. Croix, an explorer who drowned at the mouth of the river late in the seventeenth century. Another account credits Father Hennepin with giving this region the French name Ste Croix (Holy Cross) because of the burial markers located at the mouth of the river.
La Pointe County (now extinct, see Bayfield County) was created from the northern portions of Wisconsin Territory's St. Croix County on February 19, 1845. When Wisconsin was admitted into the union as a state on May 29, 1848, the territorial St. Croix County was further divided, with the territory from the Mississippi River to the current border of Minnesota continuing as de facto Wisconsin Territory until on March 3, 1849, it and unorganized federal territory lying north of Iowa were used in the creation of the Minnesota Territory. Itasca, Washington, Ramsey and Benton Counties were created by the Minnesota Territory on October 27, 1849 from the de facto Wisconsin Territory that had been separated from the Wisconsin Territory's La Pointe County.
On June 12, 1899, a deadly F5 tornado struck New Richmond. The tornado's damage path was wide and long. The tornado formed on the banks of the St. Croix River, south of Hudson. Moving to the northeast across St. Croix County, the tornado passed through the villages of Burkhardt and Boardman before striking New Richmond head on, destroying a vast majority of the town. The storm continued on towards the northeast, narrowly missing the town of Deer Park before crossing into Polk County, where it again narrowly missed the town of Clear Lake, before striking the towns of Richardson and Clear Lake. Once the tornado passed into Barron County, it struck the town of Arland before breaking up southwest of Barron. The tornado killed 117 people in St Croix, Polk and Barron Counties, 64 in New Richmond alone. It has since been established as the 9th deadliest tornado in U.S. history.