What is the value of a 1909 liberty quarter?

Both the 1909 and the 1909-O (the mintmark if any will be on the back of the coin under the eagle) are better date coins. The 1909 is worth about $8 if worn, and the 1909-O is worth about $15 if worn. The Barber series is filled with condition rarities where even common dates can be worth hundreds of dollars if uncirculated.

Without seeing your coin I can't give a full value, but in better shape both the 1909 and 1909-O can be worth $50 or more.