IFES -- International Foundation for Electoral Sytems
Although this has an international, country-level, focus, it also includes some sub-national US data.
About the IFES: "The International Foundation for Electoral Systems (IFES) supports citizens’ right to participate in free and fair elections. Our independent expertise strengthens electoral systems and builds local capacity to deliver sustainable solutions." Includes:
- Public Opinion Surveys
"Through IFES' Applied Research Center, public opinion research approaches are developed for each country context, with no one-size-fits-all approach. This method has unearthed findings across the globe on voter education, elections, government, social status and much more.
An example of IFES' long-standing work in public opinion is the annual Ukraine survey. IFES has conducted 19 surveys in Ukraine..."
- Election Resource Center
"The ERC contains thousands of key electoral documents – including ballots, country reports, electoral codes, civic education posters and more.