SR 142 begins in
McNairy County in
Selmer at an intersection with
US 45/
SR 5 south of downtown. It goes east to leave Selmer and pass through first farmland, then wooded areas, to pass through
Stantonville, where it has a short concurrency with
SR 224. The highway then turns southeast to pass through
West Shiloh, where it has an intersection with
SR 117, before crossing into
Hardin County.{{cite web|url=https://www.tn.gov/content/dam/tn/tdot/maps/county-maps-(us-shields)/h-m/McNairy%20County.pdf|title=Map of McNairy County ==Major intersections==