At the time of the Polish-Lithuanian Commonwealth (16th–18th century), the area now known as Szydłowiec Powiat was part of the historical region of Lesser Poland. In 1553, Mikołaj Radziwiłł established a county, which then included the Szydłowieckie and Skarżyskie demesnes. This area comprised the town of Szydłowiec, a few farming villages and about a dozen forest settlements involved in the production of iron, glass, tar and potassium (Stara Wieś, Długosz, Jankowice, Wysoka, Zdziechów, Szydłówek, Sadek, Skarżysko Książęce, Posajdów, Ciechostowice, Huta, Mroczków, Olszyny, Młyn, Orońsko). In 1622, the county comprised 19 villages, the mills near Rybianka, two smithies (Duraczów and Mroczków) and two glassworks (Majdów, Jakubek). The Radziwiłł family owned the Szydłowieckie demesne until 1802, but did not reside in Szydłowiec. The county was administered by governors, starosts and tenant farmers.

Following the death of Maciej Radziwiłł in 1800, the estate was auctioned by the Austrian government and bought by princess Anna Sapieha, who sold it to the treasury of the Kingdom of Poland in 1828. In 1809–1866 the Szydłowiec powiat included the government demesnes of Bodzentyn, Samsonów and Suchedniów, constituting a large part of the Old-Polish Industrial Region.

The powiat as an administrative unit was introduced in Poland in the second half of the 14th century, replacing the formerly used castellanies. Each area (consisting of 2-3 court districts) was assigned a district court which had no formal seat, but instead travelled around and held proceedings in major local centres (usually towns). The areas around those centres (whose inhabitants were the subjects of the district courts) became powiats. Their governors (known as starosts from the 15th century onwards) were responsible for the collection of taxes and the execution of court verdicts, and served as judges in cases of public order violations.

When West Galicia was annexed by the Duchy of Warsaw (in 1809), Szydłowiec became the powiat town of the newly created Radom Department (by decree of the Duke of Warsaw, Frederick Augustus I of Saxony, issued on 17 April 1810).

In 1815, when the Russia-dependent Kingdom of Poland was created, the Szydłowiec Powiat became part of the Opoczno District in the Sandomierz Voivodeship, which then became the Sandomierz Governorate in 1837, then the Radom Governorate in 1844).

From 1842 to 1866, as a result of administrative changes, the former Szydłowiec Powiat was designated as a “district” within the Opoczno Powiat.

On 1 October 1954, the Szydłowiec Powiat was re-established. It became part of the Kieleckie Voivodeship.

The Szydłowiec Powiat in its present form was established on 1 January 1999, as part of the Masovian Voivodeship.