This isn't a full-time population, but the Zulu Kingdom had an annual umKhosi Festival --a Festival of First Fruits-- where almost the entire population came together at the capital for a series of religious, military, civil, state, and economic rites, rituals, and proclamations, all of which was meant to cleanse the attendees of evil spirits and ensure a good harvest. If you could go, you went. Now how many people owed their allegiance to the Zulu king at different points in the Kingdom's history is often just an educated guess, but for ten days or so every year, the Zulu capital (Shaka, Dingane, Mpande, and Cetshwayo all built their own capitals) would easily have cleared your 200,000 threshold. Typically only the extended royal family and one or two of the king's favourite regiments actually slept in the capital-proper, but there were plenty of other towns within line of sight of the capital to house visitors, so if we are prepared to call them suburbs, we can definitely say there were permanent structures capable of housing hundreds of thousands.

As long as I'm writing, I might digress slightly to say so concentrated was the Zulu Kingdom during that festival that rinderpest epidemics and other cattle plagues hit them much harder than the Boer/Afrikaaner and British neighbours. In a land where cattle is wealth to the point where every home and town is built around a cattle kraal, a conspicuous display of wealth is to show off your cattle at the umKhosi Festival. Now contagious livestock is in close proximity to much of the rest of the Kingdom's cattle population. It could be a real problem.

Source: John Laband's The Rise & Fall of the Zulu Nation goes on at great length about the unKhosi Festival. In the life of the kingdom, most important conversations and decisions happened during one. His history probably mentions 30 in detail.