| Ostrów County | |
| Native Name: | Powiat ostrowski |
| Settlement Type: | County |
| Total Type: | Total |
| Image Map1: | POL powiat ostrowski map.svg |
| Map Caption1: | Division into gminas |
| Mapsize1: | 100px |
| Subdivision Type: | Country |
| Subdivision Type1: | Voivodeship |
| Subdivision Name1: | Masovian |
| Area Total Km2: | 1218.06 |
| Population Total: | 72558 |
| Population As Of: | 2019 |
| Population Density Km2: | auto |
| Population Urban: | 24430 |
| Population Blank1 Title: | Rural |
| Population Blank1: | 48128 |
| Coor Pinpoint: | Ostrów Mazowiecka |
| Coordinates: | 52.8°N 75°W |
| Seat: | Ostrów Mazowiecka |
| Parts Type: | Gminas |
| Parts: | Total 11 (incl. 1 urban) |
| P1: | Ostrów Mazowiecka |
| P2: | Gmina Andrzejewo |
| P3: | Gmina Boguty-Pianki |
| P4: | Gmina Brok |
| P5: | Gmina Małkinia Górna |
| P6: | Gmina Nur |
| P7: | Gmina Ostrów Mazowiecka |
| P8: | Gmina Stary Lubotyń |
| P9: | Gmina Szulborze Wielkie |
| P10: | Gmina Wąsewo |
| P11: | Gmina Zaręby Kościelne |
| Blank Name: | Car plates |
| Blank Info: | WOR |
| Website: | http://www.powiatostrowmaz.pl |
Ostrów County (Polish: powiat ostrowski) is a county in Masovian Voivodeship, east-central Poland. Its seat is located in the town of Ostrów Mazowiecka, with the only other town of the county being Brok. The county was established on 1 January 1999, and historically existed from 1919 to 1939 in the Białystok Voivodeship, Second Polish Republic, and in 1939, in the Warsaw Voivodeship.
The county covers an area of 1218.06km2. As of 2019, its total population is 72,558, out of which the population of Ostrów Mazowiecka is 22,489, that of Brok is 1,941, and the rural population is 48,128.[1]
Ostrów County is bordered by Łomża County to the north, Zambrów County to the north-east, Wysokie Mazowieckie County to the east, Sokołów County and Węgrów County to the south, Wyszków County to the south-west, and Ostrołęka County to the north-west.
The county is subdivided into 11 gminas (one urban, one urban-rural and nine rural). These are listed in the following table, in descending order of population.
| Gmina | Type | Area (km2) | Population (2019) | Seat |
| Ostrów Mazowiecka | urban | 22.1 | 22,489 | |
| Gmina Ostrów Mazowiecka | rural | 283.7 | 12,885 | Ostrów Mazowiecka * |
| Gmina Małkinia Górna | rural | 134.1 | 11,617 | Małkinia Górna |
| Gmina Wąsewo | rural | 119.2 | 4,317 | Wąsewo |
| Gmina Andrzejewo | rural | 118.6 | 4,094 | Andrzejewo |
| Gmina Stary Lubotyń | rural | 109.2 | 3,724 | Stary Lubotyń |
| Gmina Zaręby Kościelne | rural | 88.9 | 3,660 | Zaręby Kościelne |
| Gmina Brok | urban-rural | 110.2 | 2,840 | Brok |
| Gmina Nur | rural | 102.9 | 2,670 | Nur |
| Gmina Boguty-Pianki | rural | 89.1 | 2,594 | Boguty-Pianki |
| Gmina Szulborze Wielkie | rural | 46.7 | 1,668 | Szulborze Wielkie |
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