I think something that could be quite important to think about here is also that you don't want the populace to lose the chips implanted inside of them. There are quite a few job or hobby related incidents in which people lose digits are even entire limbs, like their legs or arms. Because of that, it could theoretically be considered a bad choice to place the chips here, unless of course you go with the idea that the government predetermines the chipped people's jobs as well.
In that case, you could decide that people in low risk jobs could get implanted in their arms or legs, and other people could get implanted somewhere else. It's that "somewhere else" bit that gets even more opinionated. Like others have stated, while it would be arguably easy to place a chip inside the head of a baby, it wouldn't necessarily be easy to pull the chips out later in life. A chip placed in front of, or near, a vital organ could result in pieces of the chip doing damage to the organs themselves if the chipped person is ever shot or stabbed in that area. 238
Likewise, putting the chip in other areas, like under the arms or lower belly area could make sitting down or becoming overweight quite uncomfortable, depending on the size of the chip. Putting it in the back could make sleeping harder.
I suppose everything comes down to the size of the chip, whether or not it has to be removed in order to be verified (could officials simply scan the chip through the skin with an electronic device?), and how visible it must remain at all times.
However, as a side note I'd like to point to two chip-ish instances in video games: The location of <PERSON> in Master Chief's head in Halo, and the bar code on the back of <PERSON>'s head in Hitman. Depending on your own rules, this area of the head could be a viable place to put the chip. There's a lot of ways to play with that idea. Put a small disk tray like device back there, or force the populace to keep their heads shaved. Overall, I'd still say that this can be kind of a difficult question to answer with so many variables. 477