Depending on where you were in the world during the early 19th century, city life had differing particularities. There were some general similarities, though, as urbanization was rapidly increasing during and after the Industrial Revolution. In general, people in cities had more opportunities available to them and a relatively more stable lifestyle than someone from the country. However, living conditions were very poor for all but the upper class.
First, it is important to address the population growth in cities. During the Industrial Revolution, many people moved to cities to find work in a factory or other industrial setting. One of the positive aspects of population growth was that employment rates also went up. Demand for and production of goods was increasing, which is good in a capitalist economy. People were also receiving a wage for their work, as opposed to subsistence-based work and economy.
Unfortunately, work in early industrial settings was highly dangerous. Children were often employed in large numbers because they demanded a lower wage and could fit inside machinery for cleaning and repairs. Wages for both adults and children were quite low, and this sparked the development of labor unions. Labor conditions were also made dangerous by the materials being used- dangerous substances like asbestos, arsenic, and phosphorous were commonplace in factories.
Urban spaces were unable to keep up with the rapid influx of people from the countryside, and cramped housing and work spaces were veritable cesspools. Poor and working class people did not have very good hygiene, so disease was common and spread quickly. Cholera killed many in the United States and United Kingdom.
As I mentioned above, there were some differing factors in city life depending on the location. There was an increasing push for bettering public health standards during this time, and in 1801, Philadelphia became the first city to provide clean water for drinking throughout the entire city.
Due to the boom in production and trade, more jobs were available in cities, as were goods which might not be available in the countryside. Unfortunately, many people were unable to afford the wealth of goods available to them due to low wages.
Massive fires were also problematic as people and buildings were crowded together. One small, accidental fire could quickly spread and take out several buildings, as in the Great Fire of 1835 in New York.