Place the sugar and the water into a medium saucepan over medium-high heat. Stir to combine. Continue to stir frequently until all of the sugar has dissolved. Remove from the heat and add the celery seed, cover and allow to steep for 1 hour. Strain though a fine mesh strainer into a heat-proof container and place in the refrigerator, uncovered until completely cool. Place in an airtight container and store for up to 6 months.
To use, add 2 tablespoons of syrup to 1 cup soda water and stir to combine.