Baulne-en-Brie is located some 15 km east by south-east of Château-Thierry and 20 km west by south-west of Épernay. It can be accessed by the D4 road from Condé-en-Brie in the west through the heart of the commune and the village and continuing east to Le Breuil. There is also a country road from La Chapelle-Monthodon in the north. The south-eastern border of the commune is part of the border between the departments of Aisne and Marne. There are three hamlets in the commune other than the village: Montchevret, Grande Fontaine, and Romandie. There are extensive forests in the north, centre, south-east and south of the commune with the rest of the area being farmland. The Verdonnelle stream flows north-west through the southern part of the commune passing near the hamlet of Romandie and continuing north-west out of the commune. The Surmelin stream flows from the south-east passing through the village and continuing north-west to join the Marne near Mézy-Moulins.
In 2010 the commune had 288 inhabitants. The evolution of the number of inhabitants is known through the population censuses conducted in the commune since 1793. From the 21st century, a census of municipalities with fewer than 10,000 inhabitants is held every five years, unlike larger towns that have a sample survey every year.
Economy
Baulne-en-Brie is an agricultural and wine-producing village and a part of the Appellation d'origine contrôlée zone for "Champagne of Aisne".
Culture and heritage
Civil heritage
The commune has two sites that are registered as historical monuments:
A Lavoir in the main street has been decorated on the theme of the fable "The dairy and milk jug".
Little Switzerland of Condé, the area around the hamlet of Romandie, gives access to the Verdonnelle valley.
A Directional table opposite the Chemin de Glapierson the road to Saint-Agnan offers an outstanding view of the Surmelin valley.
Religious heritage
The commune has several religious buildings and structures that are registered as historical monuments:
The Church of Saint Bartholomew. It has one of the last wooden ceilings with alternating grain slats in the world. The Church contains three items that are registered as historical objects:
*A Funeral Plaque of Madeleine de Castellan, widow of Louis Mallart, Counsellor to the King
