ALL John Deere riding mowers from 1963 to current day have been built by Deere.
*They do use some components from other manufacturers, such as Tuff Torq transmissions, Briggs, Kawasaki, Kohler engines...but all of them are built in John Deere factories.
There is some misinformation out on the web about MTD and maybe someone else building them. NOPE. Deere builds them.
**They even, secretly, built a tractor for Honda that was based on the LX platform. (Google, Honda HA4118 or HA4120) The tractor and mower deck are Deere, but the hood and engine are Honda.
Back in the day, Deere did use some other manufacturers to build their walk behind products (Murray, Ariens, and possibly even Noma).
Compact tractors are assembled in the factory in Augusta, GA.
Back in the day, there were some Yanmar tractors that were branded John Deere, but all current compact tractors are Deere built in Deere factories using Yanmar diesel engines.
I've worked at a Deere dealership for 23 years, hope this helps!