I figure 3rd cousins. First cousins are allowed to marry many U.S. states and countries of Europe. The risk of genetic anomaly has a lot to do with 2 people who carry allele for the same anomaly, their risk of having a child with the condition increases. However, you could marry someone from the other side of the world and it would just so happen you both carry the same genetic anomaly.
I have the allele for Tay Sachs. If I had the condition I would have died before I was 5 years old. I am 81. If I had produced children by another person who had the allele for Tay Sachs our chances of having a child with the Tay Sachs condition greatly increases.
This is in the Autosomal DNA and even siblings do not inherit Autosomal the same way. You got it 50-50 from both parents but not necessarily 25% from each of your 4 grandparents as there usually will be a bias in what you inherited from grandmother and grandfather on both sides of the family and how you inherited the bias will not be how your siblings inherited it unless you have an identical twin.
If you did you family history you will probably find closer cousin marriages among your ancestors than 3rd cousins. When people lived in small towns and the means of transportation was by some beast of burden, their chances of becoming acquainted with someone who wasn’t a cousin wasn’t very easy.