Piauhy, a N. E. province of Brazil, bounded N. by the Atlantic, E. by Ceara and Pernam-buco, S. by Bahia and Goyaz, and W. by Ma-ranhao; area, 94,500 sq. m.; pop. in 1871, 232,000. Piauhy has but 20 m. of seaboard, and only one port, at the mouth of the main stream of the Parnahyba. The face of the country, generally low in the coast region, swells toward the east and south, and culminates in the Serras Vermelha and dos Dous Irmaos, which on the boundary with Pernam-buco form a sort of narrow plateau attaining a maximum elevation of 1,500 ft. above the sea. The whole province is watered by the Parnahyba and its tributaries. The Parnahyba rises on the border of Goyaz, and flows generally N. N. E. through a more or less swampy country to the sea, into which it falls through six mouths. Its entire length is estimated at 990 m., and it is said to be navigable for 780 m. The principal affluents are the Gurgueia, Piauhy, Caninde, and Poty. The climate is hot and somewhat damp and insalubrious, particularly in the low grounds near the rivers. The soil is for the most part fertile.

The vegetation is locally distinguished into the mimosa of the east, characterized by catinga forests, with plants copiously furnished with hairs and prickles, stiff leaves, small flowers, a very tender fibre, and not unfrequently a milky juice; and the campos agrestes of the west country, in which forests of gnarled and stunted trees, palms, and open plains alternate. The pasture grounds of the last support a rich, coarse perennial grass. Agriculture is backward. The principal cultivated products are cereals, cotton, the sugar cane, mandioca, and tobacco. Cattle rearing is the chief industry of the province, and the principal manufactures are rum and sugar. The roads are extremely bad, and the means of transport very inefficient. Education receives a fair share of attention, there being, according to last reports, 68 schools, 11 of which are private, and 25 for females, with a total of 1,738 pupils, of whom 456 are females. The capital, Therezina, has a lyceum; and Oeiras and Amarante have each a college.

The only other town of importance is Parnahyba, the port, which is exceedingly unhealthy.