SR 27 begins at SR 238 in Southport and heads northeast to the town of Boothbay Harbor. It intersects SR 96, then heads north to the town of Edgecomb to US 1, where it turns left along US 1 heading into the town of Wiscasset. It intersects SR 218, and then immediately turns right and continues north to Dresden, where it intersects SR 197. SR 27 continues north to Pittston where it intersects State Route 194 and State Route 126. SR 27 continues into Randolph where it intersects SR 226 and then turns west as SR 9 continues north to Augusta.
In Augusta, SR 27 intersects SR 24 and US 201, then intersects US 202, SR 11, SR 17 and SR 100 at a rotary. Continuing north, SR 27 leaves US 201 and turns northwest toward Belgrade. It intersects SR 105 and SR 104 before heading towards I-95 along with SR 8 and SR 11. In North Augusta, the highway intersects SR 3 and, in Sidney, intersects SR23. In Belgrade, SR 8 and SR 11 split off and SR 27 intersects SR 135 before passing through Belgrade Lakes Village.