This resource replaces the now defunct American FactFinder. This is the U.S. Census Bureau's main vehicle for distributing U.S. census data, including economic censuses and surveys and annual population estimates. Population, housing, economic and geographic data can be found here.
GovInfo provides free public access to official publications from all three branches of the Federal Government, with comprehensive advanced search and browse options. Some things you can find in GovInfo include: Budget of the United States, Commerce Business Daily, Congressional Directory, Congressional Record, Economic Indicators, Economic Report of the President, Government Accountability Office Reports, U.S. Government Manual, and the Weekly Compilation of Presidential Documents. GovInfo replaced FDsys in 2018.
Looking for data from a University? Most campuses have a centrally located office that tracks their data. Here is an example of BGSU's Office of Institutional Research. These offices are sometimes called different names such as Institutional Effectiveness. However, they may be willing to share datasets with graduate students.