Its been 5 years since we moved into our home and I started building up my garden soil. Its coming along great, but I don't have the space to rotate crops and am worried about a build up of pests and pathogens. So i was doing some research and I can't get a straight answer. Should I till my soil in the winter to expose pathogens to the cold (below freezing) to kill them off?

I think it depends on (a) where you are located and what kind of temperatures you expect for winter and (b) what kind of pests and pathogens are you concerned about.
For tomatoes and many other crops, you can avoid the worst of the disease buildups by removing all plant material at the end of season. I think that would be a standard advice for any crop where you cannot rotate from year to year, to get all residues out in the fall. This may also help with pest buildup, if they also overwinter where their favorite plant has been.
With regards pests I have seen tilling advice occasionally for specific pests/crops, and I recall the suggestion of winter kill but IDK if the current science is still supporting that. But if you are able to till during the winter, you probably don't get cold enough to kill anything. Most pests are pretty cold tolerant in their dormant form. Another thing I remember hearing is to turn the soil so birds can eat the pests. That might actually work if you have a big bird population around, that are insect eaters. I have robins on patrol here for the whole nesting season, but there's not a lot of action in the fall and winter. So I would be better off tilling for that purpose in spring, and leave it a week or two for them to pick over.
So if I were you, I would tailor my actions to specific pests or pathogens and time it for the climate/environment you are in.

I would not rely on cold to kill pathogens completely, it may reduce numbers a little bit, but considering that us microbiologists freeze cultures to store them over time, I would not consider it a suitable way to reduce numbers to a large degree.

Thank you, I was worried about the temperatures not being cold enough. We had a stretch of cold that wouldn't get above 28F during the day for a good month. Its been freezing for longer. It warmed up enough today, and there hasn't been any precipitation for a while, so i thought if it was worth it I could turn the soil and get ready for the next stretch of freezing weather.

Though, it sounds like i need some REALLY cold weather to do the trick.

As for the potential harm tilling could have. I've read about Nitrogen loss and soil erosion being the key ones. I won't have soil erosion with how my garden is set up and the type of soil i have, but Nitrogen loss does concern me. Thoughts on this? If it's not a big problem to till, I'll do it just to get outside with the small possibility to combat disease for next season.

PS
Another thought, UV exposure. I didn't research that yet but the thought just entered my head. Thought I mention it.

If you want to avoid N loss, you are best to till just prior to planting something, especially in fall or winter. Tillage is a big driver of N loss.
For example :
https://news.psu.edu/story/372945/2015/ ... ss-organic
Secondly, in studies involving manure spreading in fall and winter and measurements of N loss, temperature made a big difference. "As the soil temperature decreased, losses of NH4-N, organic N, and total N exponentially increased."
https://www.researchgate.net/publicatio ... pplication

So with regards N loss by tilling in winter, when you can't sow a crop, and it's going to be cold, it is a lose-lose proposition.

I didn't realize the extent of how much is lost. And for the cold to be a factor was news to me. Thankyou very much for the info, i suppose tilling during winter isn't for me.