Not on the same scale as in WWI, but yes, entrenchments had been used in conflicts before WWI, and above ground field fortifications had been used even before. Sieges often saw the digging of trenches, which combined with fortifications were meant to keep the defenders from sallying forth. Good 19th century examples of this include the Siege of Petersburg in the American Civil War, the Siege of Sevastopol in the Crimean War, and the Battles for Plevna in the Russo-Turkish War. Trenches were also dug for the Siege of Port Arthur, during the Russo-Japanese War.
Trenches as field fortifications were used in the Russo-Turkish, Second Anglo-Boer, Russo-Japanese and the Balkan Wars, to shelter units from enemy firepower. Conflicts like the American Civil War and the Franco-Prussian War had seen the use of above ground field fortifications, either purpose built or ad hoc like walls or sunken roads, and extensive field fortifications were utilized even earlier, such as the Lines of Wissembourg and the Lines of Torres Vedras, and at battles such as Borodino and Malplaquet. However, it was the developments in rifle, artillery and explosives technology from the early 1870s onwards that led to a shift towards below ground trenches that could completely shelter soldiers from enemy fire.
For sources, I'd recommend Nicholas Murray's excellent book, Rocky Road to the Great War, and I believe the thesis it's based off of can be found online. You can also watch his lecture [here] (https://www.youtube.com/watch?v=2cbq7iu8FrI).
One particularly gruesome example of pre-WW1 Trench Warfare (which also hits all the stereotypes of Trench Warfare) was the 1864 Battle of Cold Harbor in the American Civil War. The Confederate army had seized the high ground and dug some of the best trenchworks they had ever made, and Grant, after several "victories" in his ongoing Overland Campaign, had been feeling overconfident. The result was sending several infantry corps, tens of thousands of men, in neat ordered lines, into the teeth of fully entrenched Confederate riflemen and cannon firing double canister. Union casualties were 13,000 killed and wounded to 5,000 Confederate, roughly on par with the similar Battle of Fredericksburg two years earlier. It was this Cold Harbor, if I recall correctly, that got Grant the nickname "the Butcher".