A Country is the second tier of title available and landed ones are the lowest tier that is playable. On the map the territory of a Country will encompass multiple Baronies and cannot be altered.
Control represents the power a landed Count has over its County. It is decreased during sieges and when Baronies are forcefully seized and can be increased by the Marshal.
Development is the measurement of technological advancement and general infrastructure in a County. Development directly increases taxes and levies gained from holdings and unlocks some additional options. Development increases very slowly across the duration of the game and radiates outwards from high-development Counties to those nearby. It can also be increased via a Steward's Increase Development task but it is still a fairly slow process.
Popular Opinion represents the sentiment of the populace towards the Country's Count. It is decreased when the Count is of a different culture or faith compared to the Country, encouraging the use of vassals of the local culture and faith.