Reid has not been offered a new contract by the Midlands club, with his current deal set to expire.
Although West Brom struggled in the Premier League this season, narrowly avoiding relegation, the versatile 33-year-old is happy with the progress made since he joined the club towards the end of their promotion-winning Championship season in 2010.
Reid initially moved on loan from Blackburn Rovers, before completing a permanent switch after West Brom were promoted.
"Looking back at the amount of games I've played and the results we've got in those games, I can look back with pride that I've had an impact in the games I've played," Reid told the club's official website.
"It's obviously disappointing this season went as it did because the three campaigns before that were almost non-stop success with finishes of mid-table and higher.
"When I first joined obviously I was on loan in that Championship season towards the end and was lucky enough to help the club cross the line and get promoted.
"That summer was a big summer for me. I was let go by Blackburn and there were doubts about my fitness and whether I would even get back to playing regularly at the top level.
"For the club to put their faith and trust in me gave me a massive boost at that stage in my career.
"It's ended up being a great four years at the club."
Reid made 87 appearances for West Brom after joining on a permanent basis.
‘England have the players to win the World Cup – it’ll be tough for Thomas Tuchel to do a bad job, with the squad he has at his disposal’ Former Three Lions winger backs new boss after gentle qualifying draw
‘This is the hardest Manchester derby to call in years – Manchester United shouldn’t be petrified, it feels like Manchester City aren’t in control of any game at the moment’ Former Red Devils striker thinks a surprise result could be possible
