PA-28 Cherokee/Archer/Dakota/Pillan/Warrior
Flight Crew Instrument; Flight Crew Private
Flight Crew Last 90 Days 28; Flight Crew Total 730; Flight Crew Type 400
Communication Breakdown; Situational Awareness
Deviation / Discrepancy - Procedural FAR; Ground Event / Encounter Other / Unknown; Ground Incursion Runway
General None Reported / Taken
Airport; Human Factors
About 20 miles out from ZZZ I observed on ADS-B another plane landing. 10 miles out I called a 10 mile straight-in. In response; a radio call asked me if I was five minutes out from landing. I responded that I was six and a half minutes out from landing; based on GPS ETE. The response to this was garbled and I did not hear any more calls from the area. I continued the approach; calling five mile and two mile finals; as well as the ETE since someone had asked for it earlier. I could see for several miles out that the runway was clear; so at first I thought someone had position and held and had wanted to know how much time they had; and had since taken off. At about a 1 mile final I also saw an airplane and a work truck on the parking ramp and some water ponded on the left edge of the runway. As I was on very short final; less than 50 AGL; I saw a yellow tarp X in the grass off the end of the runway. Since the X was not on the runway and I had seen another plane recently land and had been asked my ETA; I then thought that workers had gotten off the runway and moved the X off the runway to allow traffic to land; so I landed. I taxied to the parking area and turned around to file a flight plan for my third leg back. While I was filing the flight plan; the other plane that had been on the ramp next to the work truck took off from the same runway. I took off shortly after him without talking to anyone on the ground; and flew back to [to home airport] without incident.That evening at home I did a web search on runway closure markings and found AC150/5340-1L.In 5.7(a)(2) of this document I read that temporary closure markings can be placed just off the end of the runway if construction requires; which I did not know; and that is when I realized the runway was actually closed. Then I checked NOTAMs and saw the runway was NOTAMed closed. Contributing factors were that I assumed if a previous plane had landed recently and taken off just after I landed; that the runway was open. I also assumed that closure markings had to be over the numbers on the end of the runway; and did not know they could be just off the end of the runway. Since someone on the ground had talked to me and not told me the airport was closed (at least not in the initial transmission before it became garbled) I assumed that the airport was open. Finally since I only did a cursory check of the weather and did not fully brief the second leg of the flight; I did not see the NOTAM that the runway at ZZZ was closed.
PA-28 pilot reported not recognizing that a runway was closed and operated in and out of the airport.