The mystery of the millipedes is solved (Hopefully).
I had called Springer Pest Solutions about a week back. The guy came out and said there really isn't anything they can do for millipedes. He said for $80, they can do a 6' boundary around the house that should keep them at bay but that would need to be done monthly. I asked him how they were getting in and he says "oh, they can get in if they want". So I wasn't convinced. I went around my entire house checking for cracks or unsealed areas. Everything looked really tight.
I went back to the idea that perhaps they are already in my house and just come out and night. I had suspected the house plants before but only gave them and initial inspection with no findings. However, this time, I got a stick and started poking into the dirt of each plant. I poked into one plant and just underneath the surface, all the dirt was basically infested with millipedes. The whole plant looked like it was moving. It was quite disgusting. We tossed the whole plant last night. This morning, I have yet to see a stray millipede.