Sebastian is a city in Indian River County, Florida, United States at the confluence of the St. Sebastian River and the Indian River. It is two …Sebastian is a city in Indian River County, Florida, United States at the confluence of the St. Sebastian River and the Indian River. It is two miles away from the Atlantic Ocean. It is the largest city in Indian River County and the biggest population center between Palm Bay and Fort Pierce. The city's economy is heavily reliant on tourism. It has numerous resorts in the local area, such as Disney's Vero Beach Resort. It is very close to many natural and scenic areas like the Pelican Island National Wildlife Refuge, Sebastian Inlet State Park, and St. Sebastian River Preserve State Park.