My answer is everywhere. The alleys, the ditches, the pound, under porches, in the middle of busy intersections. I had one foster walk into my yard and sit on my porch and stay. Another was dumped in my backyard. We find them on Facebook, Craigslist, in parking lots. We have seen them be thrown out of moving car windows. We have found them in laundry baskets, dumpsters, boxes and one was locked in a crate on dusty road. One was with her babies in an abandoned car in a salvage yard. Many times people call us but most often it is the situations I listed.
Any animal we find is scanned for a chip. If we find a chip --and usually we don't-- we do our best to contact the owner. We advertise on social media and put up flyers in the area where the animal was found. I have even walked blocks and knocked on doors looking for owners. Every attempt is made to locate the owners before they are placed in the program.
Have your pets fixed and chipped. Spaying and neutering keeps them healthier longer and chips help bring them home should they ever be lost.