Willimantic is a census-designated place located in the town of Windham in Windham County, Connecticut, United States. It is a former city and borough. Known as "Thread City" for the American Thread Company's mills along the Willimantic River, it was a center of the textile industry in the 19th century. Originally incorporated as a city in 1893, it entered a period of decline after the Second World War, culminating in the mill's closure and the city's reabsorption into the town of Windham in the 1980s. Heroin use, present since the 1960s, became a major public health problem in the early 2000s, declining somewhat by the 2010s. Though the city was a major rail hub, an Interstate Highway has never passed within ten miles, despite early plans to connect it.