| State: | TX |
| Type: | SH |
| Route: | 186 |
| Map Custom: | yes |
| Map Notes: | SH 186, highlighted in red |
| Length Mi: | 47.71 |
| Length Round: | 2 |
| Established: | 1932 |
| Direction A: | West |
| Direction B: | East |
| Previous Type: | SH |
| Previous Route: | 185 |
| Next Type: | SH |
| Next Route: | 187 |
State Highway 186 (SH 186) is a state highway in the Rio Grande Valley in Hidalgo and Willacy counties in Texas, United States, that connects U.S. Route 281 (US 281), future Interstate 69C (Future I-69C), and Farm to Market Road 1017 (FM 1017) in Linn with the Gulf of Mexico at Port Mansfield.
SH 186 begins at an intersection with US 281 (future I-69C) and FM 1917 in Linn (a census-designated place formerly known as San Manual-Linn) in Hidalgo County. (US 83 heads north toward Falfurrias and San Antonio and south toward Edinburg. FM 1017 heads west toward San Isidro, La Gloria, and Hebbronville.)
From its western terminus SH 186 travels to the southeast, passing a section of the Lower Rio Grande Valley National Wildlife Refuge, before turning to a more easterly path and crossing into Willacy County. SH 186 runs along Hidalgo Avenue in Raymondville, where it crosses Interstate 69E / U.S. Route 77. Continuing to the east, the highway passes to the south of the city of San Perlita before turning to the northeast and passing through an unincorporated section of the county. In Port Mansfield, SH 186 intersects the short Farm to Market Road 606 near its eastern terminus; the highway continues one block past this point before ending at Laguna Madre.
SH 186 was designated on December 8, 1932 along a route from Linn to Raymondville.[1] On July 15, 1935, the west end was shortened to the Willacy County line.[2] On August 1, 1936, this section was restored.[3] On July 25, 1939, it was extended east to San Perlita.[4] On May 31, 1973, the portion of SH 186 from San Perlita southward was transferred to FM 2209. SH 186 was signed, but not designated, along FM 497 instead. SH 186 was extended to its current eastern terminus in Port Mansfield on August 29, 1990, replacing FM 497.