Definition:
Made in USA = Assembled in USA where all significant parts are USA made parts.
Built in USA = Assembled in USA from USA and imported parts.
1. The higher end Burris scopes like Black Diamond, Euro, and Signature series are Made in USA.
2. US Optics are Made in USA.
3. Some Trijicon are Made in USA.
The following scopes as a minimum, are built in USA.
1. All Leupold goldring riflescopes and Redfield Revolution riflescopes are built in the USA.
2. Zeiss Conquest are built in the USA.
3. Counter Sniper optics are built in the USA, or so I have been told,
4. Nightforce are built in the USA.
5. Pentax Lightseeker are built in USA (by Burris).
6. Premier Reticle are built in USA
To complicate things, some of those companies are foriegn owned.
Burris is owned by Italian controlled Beretta Holding Company.
Zeiss is German owned
Pentax is Japanese owned
Things sometimes change so fast, it is hard to keep track. For example, Redfield scopes were made/built in the USA, until 1998, when USA manufacturing plant closed. From 1998 to about 2005, Redfield scopes were imported from Asia. In 2008, Leupold bought Redfield name from Meade, and now Redfields are built in USA.
The list is much larger on imports: Bushnell, Burris (lower end scopes like Timberline and Fullfield), Weaver, Sightron, Vortex, Mueller, Pentax (non-Lightseekers), Nikon, Zeiss (not Conquest series), Schmidt Bender, Meopta, Tasco, Simmons, Kahles, Barska, A1 optics, NCStar, BSA, Centerpoint, Clearidge, Yukon, Cabela brands, Swarovski, Falcon, Hawke, Super Sniper, Millet, .....