Understanding past climate is essential for extreme weather risk preparedness and planning. Southeast Asia suffers from an acute scarcity of historical weather observations, partly due to a lack of information on the existence and location of historical data sources. Here, we address this challenge by presenting SEA-HISTIN, the largest known inventory of historical weather data sources for Southeast Asia, cataloguing diverse materials ranging from government and institutional records, bulletins, and ship logbooks, identified across archives in the UK, Malaysia, Singapore, Indonesia, the Netherlands, Japan, and the United States. The inventory documents over 1,900 terrestrial station records and more than 10,000 marine voyages spanning roughly two centuries, with detailed metadata on location, observation period, variables, instrumentation, and data source quality compiled following international best-practice guidelines. Its relational structure separates source documents from individual stations and ships, supporting flexible extension as new record types are discovered. Beyond its scientific value for reconstructing rainfall trends, droughts, and floods, the inventory connects historical weather to broader social history, including epidemics, famines, and migration patterns shaped by climate extremes. Released as an open, versioned dataset, SEA-HISTIN is designed to guide future data-rescue priorities, foster international collaboration through initiatives such as ACRE, and make historical climate records more accessible to researchers and the public alike.