Watkins Glen isn't on the 2018 IndyCar Schedule. The historic track was added two years ago then the Boston street race fell through at the last minute. The small crowds at the 2016 & 2017 races sealed its fate. It will be replace by a return to Portland. Most of the rest of the calendar look pretty much the same.
March 9-11 St. Petersburg, FL
April 6-7 Phoenix Raceway, AZ
April 13-15 Long Beach, CA
April 20-22 Barber Motorsports Park, AL
May 11-12 GP of Indianapolis, IN
May 15-27 Indianapolis 500, IN
June 1-3 Dual in Detroit, MI (2 races, Sat. & Sun)
June 8-9 Texas Motor Speedway, TX
June 22-24 Road America, WI
July 7-8 Iowa Speedway, IA
July 13-15 Toronto, ON, Canada
July 27-29 Mid-Ohio SportsCar Course, OH
Aug. 18-19 Pocono Raceway, PA
Aug. 24-25 Gateway Motorsports Park, IL
Aug. 31-Sept. 2 Portland International Raceway, OR
Sept. 14-16 Sonoma Raceway, CA
http://autoweek.com/article/indycar/portland-international-replaces-watkins-glen-2018-indycar-series-schedule