The US Census Bureau has wonderful shapefiles of all the US states and counties available – they’re referred to as TIGER/Line files. Some files are nation-based, some are state-based, and others have county-based data, but most have some combination of two. Every shapefile has an associated GEOID which can be used to link the US Census demographic data. (Check American Fact Finder to locate these datasets – they can be very specific, so match your GEOID carefully!) These shapefiles have myriad uses for essentially all kinds of demographic mapping. Bonus – shapefiles of all the US territories are available, too. The date range of the data is 1992-2019, but the data is more detailed on census years. If you’re looking for ready-made shapefiles of any US area, this is a fantastic place to look.
The USGS collects a huge amount of satellite imagery for mapping uses. You can search by address, feature, or coordinates, and the data is filterable by date. Check out the “Data Sets” tab to see all the sources you can pull from including Aerial Imagery, Commercial Satellites, Landsat, and Radar. These maps are excellent for evaluating vegetation, changes in sea level, etc. Remember that though these datasets do their best to select the clearest imagery, it’s always a good idea to download a few days in a row to ensure you don’t get an image with too much cloud coverage. This is USGS, but most datasets are global, so don’t hesitate to check even for non-US data.