How often is orthoimagery in The National Map updated and what are the acquisition dates?

Orthoimagery (georectified aerial photography) available through The National Map Downloader and The National Map Services is from the USDA Farm Service Agency's National Agricultural Imagery Program (NAIP), which is 1-meter resolution. Generally, NAIP imagery is refreshed on a 3-year cycle with approximately one third of the continental U.S. flown each year. 

The month and year of imagery acquisition can be found in the "Info/Metadata" links in the product search. The acquisition date is also part of the file name.

Learn more: USGS National Geospatial Program Imagery