Books are shelved in the Northwest Iowa Community College Library using the Library of Congress Classification System.
The following is a brief outline of classes and major subclasses.
| Call Number | Subject Area |
| A | General Works |
| AZ | History of Scholarship |
| B | Philosophy, Psychology, Religion |
| B | Philosophy (General) |
| BC | Logic |
| BD | Speculative Philosophy |
| BF | Psychology, Parapsychology |
| BH | Aesthetics |
| BJ | Ethics, Social Usages, Etiquette |
| BL | Religions, Mythology |
| BM | Judaism |
| BP | Islam, Bahaism, Theosophy |
| BQ | Buddhism |
| BR | Christianity |
| BS | Bible |
| BT | Christianity: Doctrinal Theology |
| BV | Christianity: Practical Theology |
| BX | Christian Denominations |
| C | Auxiliary Sciences of History |
| C | General |
| CB | History of Civilization |
| CC | Archaeology |
| D | History: General and Old World |
| D | General |
| DA | Great Britain |
| DB | Austria, Hungary |
| DC | France |
| DD | Germany |
| DE | Mediterranean Region |
| DF | Greece |
| DG | Italy |
| DH | Low Countries: Belgium, Luxemburg |
| DJ | Netherlands |
| DJK | Eastern Europe |
| DK | Former Soviet Republics, Russia (Federation), Poland |
| DL | Northern Europe, Scandinavia |
| DP | Spain, Portugal |
| DQ | Switzerland |
| DR | Balkan Peninsula, Turkey |
| DS | Asia |
| DT | Africa |
| DU | Oceania, Australia, New Zealand, Hawaii |
| DX | Gypsies |
| E | United States of America: General Works and History |
| F | United States Local History, Canada, Latin America |
| G | Geography, Anthropology, Recreation |
| G | General Atlases, Maps |
| GA | Mathematical Geography, Cartography |
| GB | Physical Geography |
| GC | Oceanography |
| GE | Environment |
| GF | Human Ecology, Cultural Geography |
| GN | Anthropology |
| GR | Folklore |
| GT | Manners and Customs |
| GV | Recreation, Sports, Games |
| H | Social Sciences |
| H | General |
| HA | Statistics |
| HB | Economics |
| HC | Economic History |
| HD | Land, Agriculture, Industry, Labor |
| HE | Transportation, Communications |
| HF | Commerce |
| HG | Finance |
| HJ | Public Finance |
| HM | Sociology |
| HN | Social History |
| HQ | Family, Marriage, Women, Children, Youth, Aged |
| HS | Societies, Clubs |
| HT | Communities, Classes, Races |
| HV | Social Pathology, Social Service, Criminology |
| HX | Socialism, Communism |
| J | Political Science |
| J | General |
| JC | Political Theory, The State |
| JF | Constitutional History: General |
| JK | Constitutional History: United States |
| JL | Constitutional History: Canada, Latin America |
| JN | Constitutional History: Europe |
| JQ | Constitutional History: Asia, Africa, Oceania |
| JS | Local Government |
| JZ | International Relations |
| K | Law |
| K | General |
| KD | United Kingdom, Ireland |
| KE | Canada |
| KF | United States |
| KZ | International Law |
| L | Education |
| L | General |
| LA | History of Education |
| LB | Theory and Practice of Education |
| LC | Special Aspects of Education |
| M | Music |
| M | General |
| ML | Literature of Music |
| MT | Music Instruction |
| N | Fine Arts |
| N | Visual Arts (General) |
| NA | Architecture |
| NB | Sculpture |
| NC | Drawing |
| ND | Painting |
| NE | Print Media |
| NK | Decorative Arts, Applied Arts |
| NX | Arts in General, Visual and Performing Arts |
| P | Language and Literature |
| P | Philosophy and Linguistics |
| PA | Classical Languages and Literature |
| PC | Romance Languages |
| PE | English Language |
| PF | Dutch, German |
| PG | Slavic Languages |
| PL | East Asian Languages |
| PN | Literature, General Literary History and Collections, Performing Arts |
| PQ | Romance Literature |
| PR | English Literature |
| PS | American Literature |
| PT | Germanic Literature |
| Q | Science |
| Q | General |
| QA | Mathematics, Computer Science |
| QB | Astronomy |
| QC | Physics |
| QD | Chemistry |
| QE | Geology |
| QH | Natural History, Biology |
| QK | Botany |
| QL | Zoology |
| QM | Human Anatomy |
| QP | Physiology |
| QR | Microbiology |
| R | Medicine |
| R | General |
| RA | Public Aspects of Medicine |
| RB | Pathology, Diseases |
| RC | Internal Medicine |
| RD | Surgery |
| RE | Ophthalmology, Eye |
| RF | Otolaryngology, Ear, Nose, Throat |
| RG | Gynecology, Obstetrics, Women, Childbirth |
| RJ | Pediatrics, Children |
| RK | Dentistry, Teeth |
| RL | Dermatology, Skin |
| RM | Therapeutics, Pharmacology |
| RS | Pharmacy |
| RT | Nursing |
| RZ | Other Systems of Medicine |
| S | Agriculture |
| S | General |
| SB | Plant Culture |
| SD | Forestry |
| SF | Animal Culture |
| SH | Aquaculture, Fishing, Angling |
| SK | Hunting |
| T | Technology |
| T | General |
| TA | Engineering: General and Civil |
| TC | Hydraulic Engineering |
| TD | Environmental Technology, Sanitary Engineering |
| TE | Highway Construction |
| TF | Railroad Construction |
| TG | Bridge Construction |
| TH | Building Construction |
| TJ | Mechanical Engineering, Mechanical Machinery |
| TK | Electrical Engineering, Electronics |
| TL | Motor Vehicles, Automobiles, Aeronautics, Astronautics |
| TN | Mining Engineering, Metallurgy |
| TP | Chemical Technology |
| TR | Photography |
| TS | Manufacture |
| TT | Handicrafts, Arts and Crafts |
| TX | Home Economics |
| U | Military Science |
| V | Naval Science |
| Z | Bibliography: Library Science |