Essential parts of Chicago's regional infrastructure appeared in 1848: the completion of the Illinois and Michigan Canal, the inception of the city's first railroad, the first telegraph connection, the founding of the Chicago Board of Trade. With approximately 20,000 people Chicago had not yet reached regional dominance, but these developments contributed to its future as a major world city and the leading metropolis of the Midwest.

The canal opened in April, after twelve years of intermittent construction, placing Chicago in the midst of a water route connecting the Gulf of Mexico and the Mississippi River to the Great Lakes and North Atlantic Ocean. Like the Erie Canal, and unlike other canal projects, it was a tremendous success, and remained so for several critical decades of Chicago's swift growth.

In January a telegraph line connected Chicago to Milwaukee, and by the end of the year Chicago was part of a network linking all the major Eastern cities. Business leaders welcomed the speed with which news from Eastern markets now reached them.

Overland transportation progressed more slowly. New wooden plank roads helped farmers bring their harvest to the city, but the roads were diffi cult to maintain. By the end of 1848 the Galena & Chicago Union Railroad track extended just 10 miles west. Within three years, however, Eastern rail lines arrived, and planning for the Illinois Central and other lines was underway. Within a decade Chicago would be the rail hub of the United States.

Transportation and economic developments fueled population growth. The Protestant Yankees who had predominated after displacing Indians in the early 1830s were joined by Irish, German, and other European immigrants, who would soon play a signifi cant role in Chicago politics and culture. Religious, racial, and ethnic diversity have characterized Chicago since the 1840s; symbolic turning points include the establishment of Chicago's Roman Catholic diocese in 1843, the founding of Quinn Chapel, Chicago's oldest black church, in 1847, and the founding of Kehilath Anshe Mayriv, Chicago's first Jewish congregation, also in 1847.

While most enterprises were partnerships or family businesses, after 1848 the scale of industry and commerce began to change dramatically, and with it the city's class structure. Cyrus McCormick moved his reaper manufacturing business to Chicago from Virginia in 1847 and sought capital for expansion. With 33 hands in 1848, the McCormick firm was already one of the largest employers; two years later it employed 150, with continued growth. The later development of Chicago's vast stockyards and meatpacking plants, its lumber yards, its steel mills, its neighborhoods, its industrial workers and labor conflicts: all can be seen in retrospect as emerging from Chicago's turning point in 1848.

Douglas Knox and Michael Conzen