The Haibara District is composed of Kawane-honchō (川根本町) up north and Yoshida Town (吉田町) along the coast. It used to include Makinohara City (牧之原市) along with portions of Shimada City (島田市) and Omaezaki City (御前崎市), but redistricting has since seen these cities branch off, hence the large gap. If you check out Makinohara, you can see a few post offices there still bear the name Haibara.

すみよし

住吉郵便局

Left: Yoshida Town mascot Yoshi-kichi (よし吉).
Right: An eel since eels are farmed in the area.

よしだ

吉田郵便局

Left: Yoshida Town mascot Yoshi-kichi (よし吉).
Right: An eel since eels are farmed in the area.