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Partitions and development (1815–1918)

In 1820, the government of the Congress Kingdom designated Łódź and its rural surroundings for centrally planned industrial development. Rajmund Rembieliński, head of the Administrative Council and prefect of Masovia, became the president of a commission that subdivided the works two major phases; the first (1821–23) comprised the creation of a new city centre with an octagonal square (contemporary plac Wolności; Liberty Square) and arranged housing allotments on greenfield land situated south of the old marketplace; the second stage (1824–28) involved the establishment of cotton mill colonies and a linear street system along with an arterial north-south thoroughfare, Piotrkowska. Many of the early dwellings were timber cottages built for housing weavers (domy tkaczy).

During this time, a sizeable number of German craftsmen settled in the city, encouraged by exemptions from tax obligations. Their settlement in Poland was encouraged by renowned philosopher and statesman Stanisław Staszic, who acted as the director of the Department of Trade, Crafts and Industry.

In 1851, the Imperial authorities abolished a customs barrier which was imposed on Congress Poland following the failed November Uprising (1830–1831). The suppression of tariffs allowed the city to freely export its goods to Russia, where the demand for textiles was high. Poland's first steam-powered loom commenced operations at Ludwik Geyer's White Factory in 1839. During the first weeks of the January Uprising (1863–1864), a unit of 300 Polish insurgents entered the city without resistance and seized weapons, and later on, there were also clashes between Polish insurgents and Russian troops in the city. In 1864, the inhabitants of adjacent villages were permitted to settle in Łódź without restrictions. The development of railways in the region was also instrumental in expanding the textile industry; in 1865 the Łódź–Koluszki line, a branch of the Warsaw–Vienna railway, was opened, thus providing a train connection to larger markets. In 1867, the city was incorporated into the Piotrków Governorate, a local province.

The infrastructure and edifices of Łódź were built at the expense of industrialists and business magnates, chiefly Karl Wilhelm Scheibler and Izrael Poznański, who sponsored schools, hospitals, orphanages, and places of worship. From 1872 to 1892, Poznański established a major textile manufactory composed of twelve factories, power plants, worker tenements, a private fire station, and a large eclectic palace. By the end of the century, Scheibler's Księży Młyn became one of Europe's largest industrial complexes, employing 5,000 workers within a single facility. The years 1870–1890 saw the most intense industrialisation, which was marked by social inequalities and dire working conditions. Łódź soon became a notable centre of the socialist movement and the so-called Łódź rebellion in May 1892 was quelled by a military intervention.

The turn of the 20th century coincided with cultural and technological progress; in 1899, the first stationary cinema in Poland (Gabinet Iluzji) was opened in Łódź. In the same year, Józef Piłsudski, the future Marshal of Poland, settled in the city and began printing the Robotnik (The Worker; p. 1894–1939), an underground newspaper published by the Polish Socialist Party. During the June Days (1905), approximately 100,000 unemployed labourers went on a mass strike, barricaded the streets and clashed with troops. Officially, 151 demonstrators were killed and thousands were wounded. In 1912, the Archcathedral of St. Stanislaus Kostka was completed and its tower at 104 metres (341 ft) is one of the tallest in Poland.

Despite the impending crisis preceding World War I, Łódź grew exponentially and was one of the world's most densely populated industrial cities, with a population density of 13,200 inhabitants per square kilometre (34,000/sq mi) by 1914. In the aftermath of the Battle of Łódź (1914), the city came under Imperial German occupation on 6 December. With Polish independence restored in November 1918, the local population disarmed the German army. Subsequently, the textile industry of Łódź stalled and its population briefly decreased as ethnic Germans left the city.