Louis first headed for Lille when he left Paris on 19 March. It was conveniently located - within reach of the Channel ports or the Belgian border should it be necessary to go into exile once more. He reached Lille on 22 March, having been well received in Beauvais and Abbeville en route. But the garrison in Lille was hostile to the royal cause and Louis realised that the town couldn’t become an alternative seat of government. His only option was to leave the country.
In a letter to Talleyrand dated 26 March, Louis justified his decision to leave France on the grounds that the troops had all gone over to ‘Buonaparte’, even if he, the King, still had the hearts of the French. Once he had decided to head to Belgium, Louis disbanded the Maison du Roi, his household troops, as he could not afford to maintain them. Only those wealthy enough to support themselves followed the King into exile. He went first to Ostend but then decided to make Ghent his residence in exile. Louis arrived in Ghent on 31 March 1815 and stayed in the house of Jean-Baptiste d'Hane-Steenhuyse (seen here), which is now a museum. At times to the chagrin of the owner and his family, Louis set up his court there for the rest of the 100 Days. The writer Helen Maria Williams writes about how the Royalist supporters in Paris used to sing a song about 'notre père de Gand' (our father in Ghent) which the police had to let pass because the phrase orally sounds the same as 'pair de gants' (pair of gloves), and therefore inoculous.
Further reading:
Correspondance inédite du Prince De Talleyrand et du roi Louis XVIII pendant le congrès de Vienne : publiée sur les manuscrits conservés au dépôt des Affaires étrangères / avec préface, éclaircissements et notes par M. C. Pallain (1881)
available on Gallica here