The existing land uses in the municipality are categorized into: Urban Use Areas (residential, commercial, infrastructure/utilities, institutional, parks/playgrounds and industrial), Agriculture, Forest and Forest Use, Agro-Industrial, Tourism, Other Uses (cemeteries, dumpsite/sanitary landfill, vacant lands) and Water Uses.

Agricultural lands dominate the landscape of the municipality with a total aggregate area of 12,014.87 hectares or 79.57% of the total land area. The agricultural lands are primarily devoted to permanent crops of palay, coconut and other crops. Vegetables, citrus, fruit trees, bananas and root crops are either found in areas not planted to permanent crops or serves as intercrop on coconut lands. Agricultural lands can be found in all barangays except in the urban barangays of San Julian, San Juan and San Agustin.

The second dominant land use is forestlands with an approximate area of 2,336.71 hectares or 15.48% of the total land area. Lands with forest cover include protection lands or NIPAS areas which is part of the BVNP with an area of 1,045.7132 hectares located in Cogon. Significant forest cover in non-NIPAS areas can be found in BVNP buffer zones in Cogon, Monbon, Bagsangan, Patag and Mapaso, in Mt. Jormajam in Bolos and Cogon, in Mt. Maraot Banwa in Tabon-tabon and Cawayan. These non-NIPAS forest have an estimated area of 1,291 hectares.

Urban use areas comprise only 3.1% of the total land area or 467.159 hectares. Residential areas covers 318.582 hectares, followed by roads and infrastructures with 90.917 hectares, institutional areas with 47.562 hectares, commercial areas with 6.861 hectares, parks and playgrounds with 3.178 hectares and industrial sites with 0.06 hectares.

The banks or easement of rivers and creeks are categorized under water uses and covers 257.75 hectares or 1.71% of the total land area. There are only 5 hectares each of land used for agro-industrial and tourism purposes. Categorized under other uses are cemeteries with 2.77 hectares, dumpsite/sanitary landfills with 1.87 hectares and vacant lots with 7.84 hectares.

The two major classifications of land in the Philippines are the alienable and disposable and the forest lands, both of which are considered lands of public domain. Alienable and disposable lands refer to those which have been declared but not needed for forest purposes. Forest lands are areas in the public domain that have been classified for forest use such as public forest, permanent forest or forest reserves, timberlands, grazing lands, game refuge and bird sanctuaries, and areas which are not yet declared alienable and disposable. Of Irosin’s gross land area, 13,037.5024 hectares or 86.35% is classified as alienable and disposable lands.

Irosin’s lands that are classified as forest lands have a total area of 2,061.4658 hectares or 13.65% of the municipal land area. The Bulusan Volcano Natural Park (BVNP) which is classified as a protected area has an area of 1,045.7132 hectares. Lands classified as timberlands can be found in Mt. Maraot Banwa, Tabon-tabon with an area of 372.0559 hectares, in Cawayan with almost 400 hectares, in Mt. Jormajan, Bolos with an area of 167.4083 hectares and in Liang with 76.4970 hectares.