Databases for finding USA demographic data:
SimplyAnalytics
A mapping, analytics, and data visualization application that makes it easy for anyone to create interactive maps and reports using thousands of demographic, business, and marketing variables.
Sage Data
Create custom, exportable charts with data points from the US Census, such as age, gender, income, etc.
DemographicsNow
Geographically customized demographic data reports and maps. Identify patterns and trends regarding household expenditures, market penetration and location of goods and services.
Social Explorer
Current and historical census data and demographic information: US Census, American Community Survey, religious membership, carbon emissions data, etc. Customizable maps, charts, and reports. Info
American FactFinder (free website)
Data about the United States, Puerto Rico and the Island Areas. Data comes from several censuses and surveys: American Community Survey, American Housing Survey, Annual Economic Surveys, Annual Survey of Governments, etc.