1,335 were built, and most operate on North American Class 2 and 3 railroads (shortlines and regionals) with very few still in service with BNSF; yet they've become very hard to find.
The EMD GP35 was originally used and meant to be a main-line freight diesel locomotive, and was also more affordable and convienient compared to GE's early Universal Series locomotives. It was the answer to the replacement of the aging EMD F Series locomotives, which were beginning to show their age. The GP35 was the first EMD diesel locomotive to introduce the modern "slanted-cab", which was used as the main style for standard cab units up until the production of the SD60, original SD70, and GP60.
Many remained in service with their respective owners, but many were eventually traded-in with EMD in favor of owning EMD's much more successful (and more favorable) GP38 and GP40 (including all their counter-parts), while many others were scrapped, retired, rebuilt, or sold-off to numerous other railroads.
The introduction of the DD35 also gave it an advantage for having less units on a long train. Hence, the experiment of using a DD35B (B-unit) sandwiched between two GP35s to avoid having over 10 units hauling the same train.
The Southern Pacific owned the largest fleet of GP35s, having over 165.
The EMD GP38, GP38-2, and the GP40 were the successors to the GP35, while the EMD SD40 and SD45 replaced the GP35's duties on mainline service (including subsequent four-axle models and types).
Since around 2003 or 2004, BNSF has been in the process of rebuilding their fleet of former BN and ATSF GP30's GP40's, and GP35's into GP39E's, GP39-3's, and GP39-2E's. Yet, the rebuilt GP30 and GP35 units have more GP38 parts on a GP35/GP30's body.
The Southern Railroad and Norfolk and Western purchased GP35s with "high-hood" style cabs.
The Chicago and Northwestern was one of the main customers to purchase "torpedo-tube" GP35's.
CSX also has as fleet of rebuilt former B&O and C&O GP35's which were converted into yard and road slugs.