Forest Grove is about 40 km (25 miles) west of central Portland, an easy 30 to 45 minute drive depending on traffic. From Portland take Highway 26 west and then OR-6 south, or follow Highway 8 (Tualatin Valley Highway) all the way through the valley -- the second route is slower but goes past the wineries.
Public transit is reasonable. The Westside Express Service (WES) runs between Beaverton and Wilsonville with a connection to TriMet bus 57, which terminates in Forest Grove and runs every fifteen to thirty minutes. Travel time from downtown Portland is about an hour and a quarter.
Portland International Airport (PDX) is about 60 km (35 miles) east. There is no direct transit; rental car or rideshare is the practical option.