In the Squier Price List dated January 1991, a surprising entry caught attention: a Squier Stratocaster made in the USA. The earliest Squier US Standard Stratocasters were manufactured in March 1989 and were exclusively sold in the USA - so they were not shipped to Europe. They were last listed in the February 1992 Price List. 
​There are many guys on various guitar forums that claim Fender started to manufacture these guitars in the USA because of the fire in the Mexican factory of Ensenada, but that fire had nothing to do with their inception because it hit the plant in 1994.

January 1991 Squier Price list

Someone believes that Fender started the production of the US Squier strats because the contracts with some of the Asian builders were running out. The truth is that we'll probably never know the origin of these guitars.​

​We can distinguish four types of US Squier Stratocasters made between early 1989 and mid-1992 based on the type and location of the serial number.  The earliest models featured a 4-digit large blocky black serial number on the front of the headstock. They were pretty rare and were soon replaced by US Squier Stratocasters that sported an all numerals serial number stamped on the neck plate starting with “00”- at first 5-digit, then 6-digit serial number. In late 1989 the serial number was moved to the headstock, so most of the US Squier strats made between late 1989 and 1992 had “E9” and “N9” series serial numbers (considering that “E9” was used for many 1990 guitars).

US Squier Strat, Model #1 (Courtesy of Claptonfan1 from Strat Talk)

US Squier Strat, Model #2 (Courtesy of Ofranciscovich)

US Squier Strat, Model #3 (Courtesy of Ricardo)

US Squier Strat, Model #4. Note the black plastic sleeve of the truss rod (Courtesy of Jack's Guitarcheology)

All US Squier Stratocasters featured the same ceramic pickups used for the first Mexican Standard Stratocasters, Ping bridges, and cast/sealed tuning machines, although a few of the very first US Squiers with the all-numerals serial number on the headstock were fitted with vintage-style tuners. Many US Squier strats were equipped with dotted knobs.

Dotted knob and cast/sealed tuning machines

Generally speaking, we can assume that the earliest US Squier Strats had a slightly smaller body with a swimming pool route, rosewood or maple cap neck without both skunk stripe and vintage style truss rod. Most of them have a penciled date on the heel of the neck with the name of the final sander or initials. 

Pool routing of a US Squier Strat. Also, note the Ping bridge with cast saddles (Courtesy of Andre from Strat Talk)

Regular routing on a US Squier Stratocaster. Note the dual ceramic bar pickups used also on Mexican strats and the small-size pots

The models with the serial numbers “E” and “N” featured a full-size body. Most of the “E” series guitars still had a vintage-style truss rod and lacked the skunk stripe, while almost all the “N” series guitars featured a standard truss rod with head adjustment and the skunk stripe.​

Some early US Squiers had necks marked “Hector Montes”. This led many people to believe they were Custom Shop necks because the same stamp is found on the neck of some Custom Shop Stratocasters of the ‘90s, but they were factory necks and early US Squiers were not prototypes made by the Custom Shop. In fact, in 1989 Hector was not working for the Custom Shop. Furthermore, their necks did not feature the circular logo typical of the early Custom Shop instruments. It’s also important to keep in mind that at that time Custom Shop didn’t have its own neck and body mills as it does today and they shared whatever the production line was doing. Sometimes Custom Shop Master Builders brought those factory necks (and bodies) and made them nicer by sanding the contours, rolling the fingerboards, or doing the rollovers on the headstock. So, having a Hector Montes neck does not mean the neck comes from the Custom Shop, but means Hector shaped that neck.​

Hector Montes stamp on the neck of an early US Squier Standard Stratocaster (Courtesy od Claptonfan1 from Strat Talk)

George Blanda recalls in an interview with Tony Bacon that “Corona-made bodies and necks were sent to the Mexican factory for painting and buffing. […] The painted bodies and necks were shipped back to Corona for final assembly. The standard for labeling a product ‘Made In USA’ is that more than 50 percent of the value must be from the USA [51% according to Dan Smith, editor’s note] and the final transformation — the assembly — must be done in the USA. So, of course, the US-made Squiers fit these criteria.”​

However, I believe George may not remember the whole story well (it could be possible, after so much time).
The headstock shape of the US Squiers was notably different from that of all other American Strats of the late '80s and '90s, that earned the nickname "pregnant" due to its pronounced lower curve. Therefore, it is unlikely that the necks were made in the USA, although they were certainly sanded at the Corona factory, as evidenced by Hector Montes’ stamp.

US Squier Strat headstock, note the lower curve (Courtesy of Andre from Strat Talk)

Headstock of an American Standard Strat, first series. Lower curve is pronounced

Moreover, looking carefully at the body of some US Squier Stratocasters it appears to be the same used for the guitars that recall the Japanese ST-40 but that had a “MADE IN U.S.A.” marking stamped into the wood at the base of the neck (see this article): same routings, same holes in the body, same back plate with middle screw holes that line up horizontally, and same neck pocket with enlarged corners. All these bodies were probably made in Ensenada.
So, the US Squier strats could have served as a trial run for the facility in Mexico, which opened in 1989, although assembly and a few steps of their manufacturing process were completed in the USA.

The middle screws of the back plate line up orizzontally (Courtesy of the House of Guitars)

Neck pocket of an early US Squier Strat. Note the enlarged corners and the small hole (Courtesy of LA Guitar Network)

Squier Standard Stratocaster made in Mexico

In 1998, Fender introduced the Squier Standard Stratocaster made in Mexico. The shape of the headstock of this guitar was notably different from that of the US Squier and resembled the “pregnant” shape of the American Standard Stratocaster and Mexican Standard Stratocaster manufactured in the late ‘80s and ‘90s. It's noteworthy that prototypes, test models, and pre-production guitars made in Ensenada in 1989 and early 1990 had a completely different headstock shape because, initially, Ensenada used Japanese machinery—Ensenada was born as a joint venture between Fender USA and Fujigen (for further details, refer to this article).

Mexican Squier Standard Stratocaster headstock. Note the pregnant shape, different from that of the US Squier, and the black plastic truss rod insert

The Mexican Squier Strat featured a gold Squier logo on the front of the headstock and a "Made in Mexico" decal with a serial number on the back. This guitar had a poplar body and was fitted with dual ceramic bar pickups, which were also used for the Mexican Standard Strat. Its covered “hexagonal” tuning machines and the electronics was likely made by Ping. 
The Squier Standard Fat Stratocaster and the Squier Standard Fat Stratocaster Floyd Rose versions were also available. 
​Finally, the Mexican Ensenada factory also produced the Squier Classic Stratocaster and the Fender Squier Series Stratocaster, both described in the next chapter.​