"The actual enumeration shall be made within three years after the first meeting of the Congress of the United States, and within every subsequent term of 10 years, in such manner as they shall by Law direct." -- Article I, Section 2 of the Constitution of the United States
The Census Bureau produces the Census as mandated by the Constitution, as well as other demographic and economic data. The data is used by the government to determine representation in Congress, allocate funding,and make decisions, but it is also available for free and available in a variety of formats for the public. You can explore the Census for your research or to discover the diversity in your community.
You are free to use the publically available data in the Census for your research, but you do need to cite it. You may find guidance in standard citation manuals, but here are a few additional sources that might help.