Remember when looking at Census data that the Bureau now injects "noise" into the data of smaller geographic areas to ensure the privacy of citizens. Census data at the State level should be accurate (because of the need to determine Congressional seats in the U.S. House of Representatives).
However, for all geographic areas smaller than the state level, the actual census data may be somewhat different than reported. And unfortunately, we don't know how much "noise" is introduced into the data to make an accurate guess as to how far off the numbers actually are. For a more detailed explanation of the Census Bureau's privacy protection policies and its effect on reported census data, check out this article from NPR: For The U.S. Census, Keeping Your Data Anonymous And Useful Is A Tricky Balance
The demographics of an area can play an important role when making decisions for your organization. If a business is trying to decide whether to offer a particular service, they want to know the size and characteristics of the potential market.
The US Census Bureau is the main source for demographic data in the United States. Most people are familiar with the decennial census, but the Census Bureau also collects a lot more data using additional surveys. They collect a lot of data about people, business and industry, health, education and more.
US Census Bureau at data.census.gov