Can a single person adopt?
Sure. I do adoptions in Texas and I have lots of single people who are licensed to adopt. The only negative thing I sometimes find is lack of parenting experience. A lot of the kids up for adoption have been abused or neglected, or both, and have developed mental, emotional and behavioral issues. If you are looking for a perfect little baby boy/girl, I’d go through a private agency. It’s much more expensive but may be the way to go. If you have experience with troubled kids and are willing to adopt a slightly older child or even a sibling group, then going through the state would be the way to go. Good luck!!
In most areas of North America (Canada and the US) single people can certainly apply to adopt and they will not be rejected on the basis of their marital status. Other factors may preclude their being able to adopt but that is unrelated to their not being married. There are one or two States however where only married people may adopt and without knowing where you are I can’t comment any further.