Saint Croix River1. A river, about 265 km (165 mi) long, rising in northwest Wisconsin and flowing generally south along the Minnesota border to the Mississippi River southeast of St. Paul.2. A river, about 120 km (75 mi) long, forming part of the boundary between eastern Maine and southwest New Brunswick, Canada. It rises in a series of lakes and flows generally southeast to Passamaquoddy Bay. In 1604 Samuel de Champlain established a colony on Saint Croix Island near the mouth of the river, but the settlement was abandoned in 1605.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.Saint Croix River n (Placename) a river on the border between the northeast US and SE Canada, flowing from the Chiputneticook Lakes to Passamaquoddy Bay, forming the border between Maine, US, and New Brunswick, Canada. Length: 121 km (75 miles) Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014