Ironfeld Keep is something of a curiosity. The unions annals do not mention who built it, nor when it was built. Nor has it held a garrison for over 70 years. And then, only for a few months.
The reasons for this are primarily that Westburg is not far from it, and the keep was not deemed worth the effort, as it lies on the very western border of the union. The unexplored lands to the west were deemed too inhospitable to be worth investing any time in – As the Forsaken land is the only thing at Ironfelds western border.